Aptus Bloomboost

Aptus Bloomboost is a liquid bloom-phase additive from Aptus Plant Tech that delivers potassium (K), sulfur (S), and boron (B) in precise ratios throughout the entire fruiting and flowering period. Unlike conventional PK boosters that lean on phosphorus, Bloomboost targets trichome density, terpene expression, flavonoid production, and structural fiber mass—supporting quality and aroma alongside yield from week 2 of flowering through harvest.

Aptus Bloomboost Specifications

Specifications confirmed from the canonical supplier record (mass_hydro, SKU AP18002) and the Aptus USA product page. Aptus Plant Tech does not publish a numeric guaranteed analysis (NPK percentages) for Bloomboost.

Specification	Value
Brand / Manufacturer	Aptus Plant Tech
Distributor (US)	Hydrofarm
SKU	AP18002
Product type	Liquid bloom-phase additive / concentrate
Active elements	Potassium (K), Sulfur (S), Boron (B)
Guaranteed analysis (NPK)	Not published by manufacturer
Application phase	Fruiting and flowering, weeks 2–8
Standard feed rate	1–2 ml per gallon (0.2–0.5 ml/L)
Foliar feed rate	4 ml per gallon (1 ml/L)
Alternate feed rate (canonical)	4–8 ml per 5 gallons, increasing weekly from week 2 of flower
Weight (this listing)	1.4991 lb
Available sizes (aptus.us)	100 ml, 250 ml, 500 ml, 1 L, 5 L, 20 L
Category path	Nutrients & Additives > Additives > Growth & Bloom Boosters

Why Choose Aptus Bloomboost

The points below are grounded in the canonical supplier description and the Aptus USA product page (aptus.us).

• Potassium, sulfur, and boron—not the typical phosphorus-potassium spike. Most conventional bloom boosters lead with phosphorus (P) alongside potassium (K). Bloomboost deliberately omits phosphorus and instead combines potassium with sulfur and boron. Potassium supports the formation of healthy, fibrous fruits and flowers, regulating cell turgor and sugar transport into developing tissues. Sulfur is a constituent of proteins, certain plant hormones, and the volatile compounds responsible for aroma—it directly participates in the biosynthesis of terpenes and oils. Boron preserves membrane integrity within maturing plant tissues, maintaining structural continuity as cell walls thicken during ripening. This three-element blend is formulated to act on quality and structure, not just mass accumulation.
• Targets trichomes, terpenes, flavonoids, and oils during flower. Aptus positions Bloomboost as a quality and flavor enhancer that optimizes a plant’s genetic expression rather than a bulk-at-all-costs supplement. The brand’s manufacturing premise is that sulfur and boron supply at precise levels during the reproductive phase supports the plant’s own synthesis pathways for secondary metabolites—the compounds that determine finished-product aroma, flavor, and resin quality. This framing makes Bloomboost relevant to growers who care as much about end-product sensory profile as about raw yield numbers.
• Designed for use across the entire flowering period, not just a single week. Many PK spike products are applied for one to two weeks at peak flower. Bloomboost is designed for continuous application from week 2 of flowering through week 8 (or harvest), with the dose increasing each week as the plant’s reproductive demand grows. This progressive-dosing model means the plant receives consistent support at each developmental stage of the flower rather than a single high-concentration event that may not align with actual peak demand.
• Highly concentrated formula reduces per-feed cost over time. Aptus’s product line philosophy—summarized in the brand tagline “Less Bottles. More Stability”—is built around concentrated inputs that achieve results at low volumes. The 1–2 ml per gallon standard feed rate and 4 ml per gallon foliar rate mean that even a 100 ml bottle covers multiple feeding cycles for small systems, and the 5 L and 20 L sizes are appropriate for commercial-scale production. Lower volume per dose means less product handling, more precise measurement, and a smaller per-liter input cost versus bulkier liquid concentrates.
• Foliar application supported, particularly in the first two weeks of flower. Aptus describes foliar spraying with Bloomboost during the first two weeks of flower as “highly beneficial.” This dual-mode delivery—root-zone and foliar—gives growers flexibility in how they introduce the product into the feeding program and provides a pathway to apply Bloomboost in systems where direct reservoir addition is restricted (such as DWC, detailed further in the Compatibility section).
• Compatible with soil, coco, peat, and most hydroponic systems with defined protocol. Bloomboost is fully compatible with soil, coco coir, and peat substrates without special handling. For recirculating hydroponic systems, Aptus provides specific protocols (add 1–2 days before water changes) to manage the organic biofilm that the product’s organic compounds can generate. This means growers on most common growing setups can use Bloomboost, provided they follow the compatibility instructions in this page.

Best Uses for Aptus Bloomboost

Use cases follow from the product’s K-S-B element profile, full-cycle application window (weeks 2–8), and system compatibility data from aptus.us.

• Soil and coco coir flowering crops where quality and aroma are the primary goal. Bloomboost is simplest to use in soil or coco coir—no biofilm management protocols apply, and it can be added directly to the feed solution at the standard 1–2 ml per gallon rate. Growers running these substrates who want to increase terpene expression, trichome density, and finished-product flavor in high-value flowering crops are the clearest target user for this product. Apply starting in week 2 of flower and increase the dose each week through week 8 or harvest.
• Supplementing an existing nutrient program without switching base nutrients. Bloomboost is an additive, not a base nutrient replacement. It layers onto any established base nutrient program—whether Aptus’s own line or a competitor brand—to provide the potassium, sulfur, and boron loading that most base nutrients do not supply at high enough levels during the flowering phase. Growers already running Earth Juice Hi-Brix Molasses or other organic additives in their bloom-phase stack can incorporate Bloomboost alongside those inputs without reformulating the whole program.
• Recirculating hydroponic systems (with biofilm management protocol). In ebb-and-flow, NFT, and drip recirculating systems, Bloomboost can be used if growers follow the Aptus-specified protocol: add the product to the reservoir 1–2 days before a scheduled water change so the organic compounds introduced by Bloomboost are flushed out before they can accumulate as biofilm on reservoir walls and irrigation lines. Growers running these systems should plan their change schedule around Bloomboost application to prevent buildup over multi-week cycles.
• Foliar spray application during early flower (weeks 1–2). The Aptus product page describes foliar application of Bloomboost during the first two weeks of flower as highly beneficial. The foliar rate is 4 ml per gallon (1 ml per liter). This is particularly useful in DWC systems where root-zone addition is not recommended (see Compatibility), allowing growers to still benefit from Bloomboost’s quality-enhancement action via leaf uptake during the early flower window. Apply foliar sprays during lights-off or in low-light conditions to minimize stress and evaporation.
• Fertigation systems (once-weekly maximum). For drip fertigation setups where the nutrient solution is delivered through a timer-controlled irrigation system, Bloomboost can be included in the reservoir at a maximum frequency of once per week. This restriction exists to prevent biofilm accumulation in the drip lines and emitters that more frequent organic inputs can cause. Paired with a Dosatron inline doser or similar injection system, the weekly dosing schedule is straightforward to maintain without disrupting other nutrient delivery intervals.
• Progressive-dose programs targeting peak harvest quality. Because the recommended protocol calls for increasing the dose each week from week 2 through week 8, Bloomboost fits naturally into structured weekly feed-schedule programs where the grower is dialing in nutrient intensity as the plant moves through bud set, bud swell, and ripening phases. Growers who keep weekly feeding logs and adjust EC/dose by stage will find the progressive-dosing approach compatible with their existing practice.

Aptus Bloomboost vs General Hydroponics Liquid KoolBloom

The two most directly comparable bloom-phase liquid additives at comparable price points are Aptus Bloomboost and General Hydroponics Liquid KoolBloom. Both are liquid concentrates applied during the flowering phase to support flower development. The differences lie in element selection, formulation intent, and application timing.

Aptus Bloomboost (this product): Supplies potassium (K), sulfur (S), and boron (B) without a phosphorus (P) spike. The formulation targets quality enhancement—trichomes, terpenes, flavonoids, and oils—in addition to increasing flower size and fiber mass. It is applied progressively across the full flowering cycle (weeks 2–8), with the dose increasing each week to match the plant’s evolving reproductive demand. Aptus does not publish a numeric guaranteed analysis for Bloomboost. Standard feed rate is 1–2 ml per gallon; foliar rate is 4 ml per gallon. Not recommended for DWC direct addition; foliar spray is the DWC-compatible delivery method. Aptus’s brand positioning is “Premium Quality. Superior Flavor.”

General Hydroponics Liquid KoolBloom (comparator): A highly concentrated phosphorus-and-potassium (PK) booster specifically designed to trigger and support the flowering phase. The formulation leads with phosphorus alongside potassium to support energy transfer, root-to-flower signaling, and essential oil production. It is typically applied during a peak flower period rather than across the entire flowering cycle. GH publishes a guaranteed analysis with specific P and K percentages. It is broadly compatible with GH’s Flora Series system and other nutrient programs. No sulfur or boron are featured as active elements; it does not target the same quality-enhancement metabolic pathways (terpene, flavonoid synthesis) that Bloomboost’s sulfur and boron supply support.

Key trade-offs:

• Bloomboost’s K-S-B formulation specifically addresses quality and aroma alongside flower mass; KoolBloom’s P-K formulation addresses energy delivery and flower triggering without the sulfur and boron components that drive oil and terpene synthesis.
• KoolBloom provides a published guaranteed analysis (numeric P and K percentages), making it easier to integrate precisely into an EC-managed nutrient program. Aptus does not publish numeric percentages for Bloomboost, which makes exact EC contribution estimation require measurement rather than calculation.
• Bloomboost is applied progressively throughout weeks 2–8 of flowering; KoolBloom is typically applied during a shorter peak-flower window, making the overall application philosophies different.
• Bloomboost has explicit DWC restrictions (foliar spray only in DWC); KoolBloom is generally compatible with all hydroponic systems including DWC when mixed into the reservoir.
• Growers whose primary goal is maximizing terpene and trichome expression in high-value flowering crops will find Bloomboost’s K-S-B approach more directly targeted at those outcomes. Growers who want a straightforward PK spike with a published guaranteed analysis for EC management will find KoolBloom more immediately predictable.

Both products serve the flowering phase; the choice turns on whether the grower’s priority is quality-metric outcomes (terpene, resin, flavor—Bloomboost) or a phosphorus-forward energy and trigger approach with a published guaranteed analysis (KoolBloom).

Compatibility & Operating Range

Compatibility data from the Aptus USA product page (aptus.us/products/bloomboost), the Aptus AU site, and the canonical supplier description.

Soil, coco coir, and peat substrates: Fully compatible without special handling. Bloomboost can be added directly to the irrigation solution at the standard 1–2 ml per gallon rate and applied through any standard watering or drip irrigation setup. No biofilm risk applies in substrate-based systems because the growing media absorbs and buffers the organic compounds before they can recirculate and accumulate.

Recirculating hydroponic systems (ebb-and-flow, NFT, drip-to-waste with recirculation): Compatible with a specific protocol. Bloomboost contains organic compounds that can form biofilm on reservoir walls, irrigation lines, and pump surfaces in recirculating systems. The Aptus-recommended approach is to add Bloomboost to the reservoir 1–2 days before a scheduled water change, so the organic material is introduced for a short period before the reservoir is drained and refreshed. Growers who change their reservoir on a weekly schedule should add Bloomboost toward the end of the reservoir cycle. Avoid letting a Bloomboost-dosed reservoir run for more than two to three days in a recirculating system without a planned water change.

Deep Water Culture (DWC): Direct addition to the DWC reservoir is not recommended by Aptus. The organic compounds in Bloomboost can cause biofilm accumulation in the root zone and on reservoir surfaces in a continuously recirculating DWC environment. For DWC systems, Aptus recommends foliar application only: 4 ml per gallon (1 ml per liter) sprayed on leaves during the early flowering weeks. This delivers the K-S-B element benefits via leaf uptake without introducing the product into the root-zone reservoir. Growers running beneficial microbe products like Advanced Nutrients Tarantula in DWC should note that biofilm-forming additives like Bloomboost are best kept out of the reservoir when live microbial populations are being maintained.

Fertigation systems: Compatible at a maximum frequency of once per week. More frequent fertigation dosing with Bloomboost risks biofilm buildup in the emitters, drip lines, and manifolds. Plan the feeding schedule so Bloomboost is included in one of the weekly fertigation events and is followed by a plain-water or base-nutrient-only cycle before the next application.

Rockwool substrates: Not recommended for high-frequency application. Rockwool’s low buffering capacity and inert mineral structure do not absorb organic compounds the way soil or coco does, and frequent Bloomboost application can lead to organic residue buildup in the slab or block. If using Bloomboost with rockwool, apply at the lower end of the dose range and limit application to once per week as a precaution.

Base nutrient program compatibility: Bloomboost is an additive and can be layered onto any base nutrient program—Aptus’s own Premium, Clean, or Soil Pro lines, or third-party bases from other manufacturers. No base nutrient compatibility exclusions are noted. Add Bloomboost after the base nutrients are dissolved in the reservoir and the initial pH/EC has been measured. Check and adjust pH and EC after all additives are mixed before feeding.

pH operating range: No specific pH window is published by Aptus for Bloomboost individually. Follow standard flowering-phase pH targets for the system type: 5.5–6.5 for hydroponic systems, 6.0–7.0 for soil. Bloomboost’s potassium and sulfur components are plant-available across the typical flowering-phase pH range when maintained within these bounds.

Storage: Store concentrated product in a cool, dry location out of direct sunlight. As with all liquid organic concentrates, avoid freezing. Seal the cap tightly after each use to prevent evaporation and contamination. Do not store pre-diluted Bloomboost solution; prepare the dosing amount fresh for each feeding.

Dosage Guidelines for Aptus Bloomboost

Dosing data from the Aptus USA product page and the canonical description text. Both sources are consistent when converted to the same units.

Standard feed rate (reservoir addition): 1–2 ml per gallon of nutrient solution (0.2–0.5 ml per liter). This is the Aptus-recommended general feeding rate for root-zone delivery in soil, coco coir, peat, and compatible hydroponic systems. In US gallon terms, the canonical description states 4–8 ml per 5 gallons—which is equivalent to 0.8–1.6 ml per gallon (or approximately 1–2 ml per gallon at the standard rounding). The dose is applied increasing from week 2 of flowering onwards, starting at the lower end and stepping up each week as the plant’s reproductive demand increases.

Increased-effect rate: The canonical description notes that for increased effect, Bloomboost may be used at 1 ml per 2.5 L (approximately 1.5 ml per gallon). This is within the 1–2 ml per gallon standard range and does not represent an exceptional spike—it is simply the upper portion of the normal feed-rate band. Aptus specifies that growers should ensure their active PPM/EC budget allows for this increased dosage before implementing, to avoid pushing the total solution EC beyond the target range for the flowering stage.

Foliar spray rate: 4 ml per gallon (1 ml per liter). Apply as a foliar spray, ideally during the first two weeks of flowering when Aptus describes foliar application as “highly beneficial.” Apply during lights-off or in low-light conditions to prevent leaf burn from the spray and minimize evaporation before the solution can be absorbed. This is the primary delivery method for DWC systems.

Application timing across the flowering phase:

• Week 1 of flower: No root-zone addition required; use foliar spray if desired (4 ml/gal) for early absorption benefit.
• Week 2 of flower: Begin root-zone feeding at the low end of the standard rate (approximately 1 ml/gal). Continue foliar spray in parallel if running foliar during weeks 1–2.
• Weeks 3–7 of flower: Increase root-zone dose each week, progressing toward the higher end of the 1–2 ml/gal range by mid-flower. Aptus specifies increasing “every week from week 2 onwards until week 8.”
• Week 8 of flower (or through harvest): Continue at the upper dose rate. Aptus states Bloomboost can be continued through harvest with no negative quality effects.

EC contribution: Because Aptus does not publish a numeric guaranteed analysis for Bloomboost, calculating the exact EC contribution per ml from label data is not possible. Growers should measure reservoir EC before and after adding Bloomboost to determine its actual contribution in their water chemistry. At the 1–2 ml per gallon rate, the EC addition is small but measurable. Start with a baseline EC reading after the base nutrients are mixed, then add Bloomboost and measure again to establish the delta for future planning.

Measuring the dose: Use a calibrated syringe or graduated pipette for measuring Bloomboost concentrate. At 1–2 ml per gallon, a 10-gallon reservoir requires 10–20 ml of concentrate per feeding. A 100 ml bottle provides 5–10 feedings for a 10-gallon system; a 500 ml bottle covers approximately 25–50 feedings at the same system size.

Recirculating system restriction: In recirculating hydroponic systems, apply Bloomboost only to the reservoir and schedule the next water change within 1–2 days of addition. In DWC, use foliar spray only. In fertigation systems, limit to once per week maximum (see Compatibility section).

How to Integrate Aptus Bloomboost into Your Feeding Schedule

Steps for incorporating Bloomboost into a weekly feeding program from early flower through harvest, drawn from the Aptus USA product page protocols and canonical dosing directions.

1. Confirm the start of the flowering phase before opening the bottle. Bloomboost is a flowering-phase additive. For photoperiod crops, confirm that you have flipped to a 12/12 (or shorter) light schedule and that preflowers are visible before beginning. For autoflowering varieties, wait until the plant has clearly entered the early blossom stage. Do not apply Bloomboost during the vegetative phase; the K-S-B element ratios are calibrated for the reproductive phase and are not designed as a vegetative-stage supplement.
2. Plan whether to use foliar application in weeks 1–2. Aptus recommends foliar spraying with Bloomboost during the first two weeks of flowering as highly beneficial. If you choose to begin with foliar application, prepare a separate spray solution at 4 ml per gallon (1 ml per liter) of clean, pH-adjusted water. Apply the foliar spray during the dark period or in dim light, covering both the top and underside of leaves. This is also the only recommended delivery method for DWC systems throughout the entire flowering period.
3. Prepare your base nutrient reservoir first. In week 2 of flower, begin root-zone addition alongside the base nutrient reservoir mix. Mix your base nutrients (Part A and Part B, or single-part base) in the reservoir at flowering-stage rates. Measure and record the baseline EC and pH. Bloomboost is an additive—it does not replace the base nutrient. The base nutrient provides the full-spectrum nitrogen, phosphorus, and micronutrient loading; Bloomboost adds the targeted K, S, and B elements on top of that foundation.
4. Measure Bloomboost concentrate with a calibrated syringe. Starting at approximately 1 ml per gallon (the lower end of the recommended range), measure the appropriate volume for your reservoir size. For a 20-gallon reservoir in week 2, measure approximately 20 ml. Add the measured concentrate to the reservoir while the recirculation pump is running or while stirring, to ensure even distribution. Do not add undiluted concentrate directly onto plant roots or substrate surfaces.
5. Verify pH and EC after adding all additives. After adding Bloomboost and any other bloom-phase additives, check reservoir pH and EC. Adjust pH to the target range for your growing medium (5.5–6.5 for hydroponic systems, 6.0–7.0 for soil). Record the delta EC contributed by Bloomboost for future reference—this helps you plan total nutrient strength across the flowering cycle without guesswork.
6. Feed on your regular schedule, increasing the Bloomboost dose each week. Apply the mixed reservoir solution at your standard feeding frequency. Each week from week 2 through week 8, incrementally increase the Bloomboost dose toward the upper end of the 1–2 ml per gallon range, matching the plant’s escalating reproductive nutrient demand. Keep notes on the dose applied each week so the ramp-up is consistent and measurable.
7. Continue through week 8 or harvest and then discontinue. Bloomboost can be continued through the final week of flowering and up to harvest with no negative quality effects, per the Aptus product page. After harvest, discontinue Bloomboost as part of the standard post-harvest cleaning protocol. Rinse measuring syringes, mixing vessels, and any irrigation components with clean water after each use session; organic concentrates left to dry in equipment can leave residue that is harder to remove later.

Sources & Further Reading