Translated and edited from the original by Grotek (Monster Bloom product page and label): Monster Bloom® - Grotek
Monster Bloom is a powdered fertilizer made by Grotek, a nutrient brand that belongs to Hydrofarm. Hydrofarm is a United States company that makes and distributes hydroponic growing equipment.
The powder dissolves in water. It supplies only phosphorus (P) and potassium (K), and it contains no nitrogen. Growers call this type of product a “bloom booster” or “PK booster”. It is used only during flowering.
You add Monster Bloom to your complete base fertilizer. It does not replace the base fertilizer. This article covers what the label says, what P and K do while the plant flowers, how the maker says to use the product, the mistakes growers make most often, and how to adjust for conditions in Thailand and Southeast Asia.
What the Label Says
Grotek’s product page gives this guaranteed analysis. That is the minimum nutrient content the maker promises:
| Nutrient | Guaranteed analysis |
|---|---|
| Total nitrogen (N) | not listed |
| Available phosphoric acid (P₂O₅) | 50% |
| Soluble potash (K₂O) | 30% |
Every fertilizer label prints three numbers for nitrogen, phosphorus and potassium. This is the NPK ratio. No nitrogen is listed here, so the ratio is 0-50-30.
The label names one ingredient: monopotassium phosphate (MKP). MKP is a salt made of potassium and phosphate, and it dissolves easily in water. That explains why the powder mixes in quickly.
Fertilizer labels give phosphorus and potassium as oxides (P₂O₅ and K₂O), not as the pure elements. Use the standard conversion factors to get the elemental figures: P = P₂O₅ × 0.436 and K = K₂O × 0.830. So 50% P₂O₅ is about 21.8% phosphorus, and 30% K₂O is about 24.9% potassium.
This difference matters when you compare Monster Bloom with a product that lists its contents as elements. Without the conversion, one product can look much stronger than it really is.
Translator’s note: These figures come straight from the label numbers above. At the label rate of about 0.32 g per litre (see the next section), Monster Bloom adds roughly 69 mg of phosphorus and 79 mg of potassium to each litre of water. That amount goes on top of whatever your base fertilizer already supplies.
What to do: Before you compare two boosters, convert both labels to the same form, either oxide or elemental. Only then decide which one supplies more P and K.
What Phosphorus and Potassium Do During Flowering
- Phosphorus is part of ATP (adenosine triphosphate), the molecule that carries energy inside plant cells. Phosphorus is also part of DNA and of cell membranes. The plant needs more of it while it builds new flower tissue.
- Potassium controls how water moves through the plant. It also controls the stomata, the tiny pores on the leaf that open and close to let air and water vapour in and out. Potassium switches on many enzymes, and it helps carry sugars and starches from the leaves to the flowers.
Grotek says the product supports four things:
- making proteins and starch
- stronger stalks and stems
- moving sugars and starches around the plant
- respiration and the leaves’ uptake of carbon dioxide (CO₂) from the air while buds develop
These are the maker’s claims about the product.
A PK booster works only when the plant is already getting a complete feed. Nitrogen, calcium, magnesium, sulfur and the micronutrients (iron, zinc, manganese and others) still have to come from your base fertilizer.
What to do: Read the label of your base fertilizer before you add any booster. Check that it lists nitrogen, calcium, magnesium, sulfur and micronutrients. If anything is missing, the booster will not make up for it.
How to Use It: The Maker’s Directions
- Mixing rate: 1 teaspoon per 5 US gallons of water (6 g per 19 L). The same rate applies to soil, soilless media and water culture.
- When to start: when buds are forming.
- How often: with every fertilizer feed during the flowering cycle.
- When to stop: 1–2 weeks before harvest.
Grotek lists the product as suitable for hydroponics, where roots grow in a nutrient solution instead of soil. Grotek also lists it for soilless media such as peat and coco coir.
After you add the powder, always measure the EC and pH of the final solution. EC (electrical conductivity) tells you how much dissolved fertilizer salt is in the water. pH tells you how acidic or alkaline the water is. Both affect how well the roots can take up nutrients.
To learn what research says about the last weeks before harvest, see Pre-Harvest Flushing: Science or Myth?
Translator’s note: One US gallon is 3.785 litres, so the label rate is about 0.32 g per litre. A teaspoon of powder can weigh more or less depending on how tightly it is packed. Weigh the powder on a digital scale that reads to 0.1 g instead of using a spoon.
| Tank volume | Monster Bloom at the label rate |
|---|---|
| 10 L | about 3.2 g |
| 20 L | about 6.3 g |
| 100 L | about 32 g |
| 200 L | about 63 g |
What to do: Write down the EC and pH of your tank before and after you add Monster Bloom, at every mix. After a few mixes you will know how much this product changes your solution. Then you can spot a wrong dose straight away.
Common Mistakes
- Overdosing: if the plant gets more phosphorus and potassium than it can use, the EC in the root zone rises. This can cause salt stress and burnt leaf tips. Too much phosphorus can also block the uptake of micronutrients such as zinc and iron. This blockage is called nutrient lockout.
- Starting too early: in the first weeks of flowering, the plant is still growing taller quickly. Growers call this the stretch. During the stretch the plant still needs nitrogen, so a nitrogen-free booster belongs to the later stage, when buds are forming.
- Using two boosters together: if you add two PK products to one tank, you double the phosphorus and potassium. This is easy to miss. Read the label of every product that goes into the tank.
- Treating it as a complete feed: Monster Bloom contains no nitrogen, calcium or magnesium.
- Skipping the pH check: MKP solutions are mildly acidic, so the pH of your tank can drop after you add the powder.
What to do: Before each flowering mix, list every product in the tank with its P and K content. If two products both supply mostly P and K, use only one of them.
Using It in Thailand and Southeast Asia
Translator’s note: The maker’s directions do not account for tropical heat. In many Thai grow rooms and greenhouses, the nutrient tank sits at 30–35 °C. Warm water holds less oxygen, so roots are already under stress. Plants in hot rooms also drink more water, so many growers run a lower EC than temperate feed charts suggest. See Running Hydroponics at 31 °C Reservoir Temperature and Why Temperate Feeding Protocols Break at 31 °C and 85% RH.
Translator’s note: Tap water and well water differ from area to area. They can also change between the dry season and the rainy season. Hard water carries a lot of calcium. When it meets concentrated phosphate, it can form a white, cloudy deposit, and the plant cannot use the nutrients locked in that deposit. Dissolve the powder in the full volume of water and stir. Never pour concentrated products straight into each other.
Translator’s note: Rainy-season air is very humid, and fertilizer powder exposed to it can turn into lumps. Close the bag tightly after every use and store it somewhere cool and dry, out of direct sun.
What to do (small-batch trial): Before you use Monster Bloom on a whole room, test it on 2–4 plants for one flowering cycle. Start at half the label rate and raise it only if the leaf tips stay healthy and the runoff EC stays steady. The trial shows you how your strain, water and climate react, and the rest of the crop is not at risk.
Translator’s note (buying and records): Ask the official distributor in Thailand where to buy, or ask other growers in the Equipment and Supplies section. Buy only sealed packs in the maker’s original packaging. Repacked powder can be mixed with something else, and you cannot check what is inside.
Ask the seller for two documents:
- the safety data sheet (SDS), which explains hazards, safe storage and first aid
- the certificate of analysis (COA), a lab report confirming the nutrient content of that batch
Fertilizers in Thailand fall under the Fertilizer Act B.E. 2518 (1975), as amended by the Fertilizer Act (No. 2) B.E. 2550 (2007). Fertilizer registration is handled by the Department of Agriculture (กรมวิชาการเกษตร). Check that the Thai label carries the registration number. For a “standard” chemical fertilizer, the label carries a notification number instead. For how to check this, see Verifying a Fertiliser Is Legally in Thailand.
If your farm is working toward GACP (Good Agricultural and Collection Practice), the standard for certified medicinal plant farms, keep the SDS and COA on file. Also record the batch number, the date and the dose of every feed. Inspectors expect to see a record for every input used on the crop.
Pack Sizes
Grotek lists Monster Bloom in 130 g, 500 g, 2.5 kg, 5 kg and 10 kg packs.
Translator’s note: At the label rate, 130 g makes about 410 L of nutrient solution, and 500 g makes about 1,580 L. Buy a large pack only if you will use it up before it absorbs moisture.
What to do: Estimate how many litres of solution you will mix across all your flowering weeks. Choose the pack size that covers that amount, then ask the distributor in Thailand which sizes they actually stock.
Questions and Discussion
If you have questions about Monster Bloom or PK boosters, post them below this topic. Include your base fertilizer, your growing medium, your tank volume, and your EC and pH readings before and after mixing. With those details, other growers can give you a specific answer instead of a general one.
Reference
- Grotek, Monster Bloom product page and label (guaranteed analysis, ingredient, directions, pack sizes). Monster Bloom® - Grotek