Translated and edited from Grotek’s product information for Monster Bloom
Monster Bloom is a fertilizer powder that you dissolve in water. You add it to the feed while your plants are flowering. Grotek makes it, and Grotek is a brand owned by the hydroponics supply company Hydrofarm.
The powder supplies only two nutrients: phosphorus (P) and potassium (K). It contains no nitrogen (N). So it cannot feed a plant by itself. You always add it on top of a complete base nutrient, which is the main fertilizer that supplies every element the plant needs.
Products like this are called PK boosters or bloom enhancers. For the full background on this product, see the complete Monster Bloom guide on this forum.
Grotek calls Monster Bloom its “classic” bloom enhancer. The company lists three main benefits: larger flower clusters, a bigger harvest and support for the ripening stage. These are the manufacturer’s claims, and the original gives no trial data to back them. To see what research says about adding extra phosphorus during flowering, read Bloom Booster Fertilizer: Does Extra Phosphorus Really Mean More Flowers?.
What the Label and Product Page Say
1. Nutrient content. Grotek’s product page gives the guaranteed analysis, which is the nutrient content the manufacturer guarantees. It lists:
- 50% available phosphoric acid (P₂O₅)
- 30% soluble potash (K₂O)
- no nitrogen
That makes the NPK ratio 0-50-30 (nitrogen, phosphorus and potassium, in that order). The label gives phosphorus and potassium in oxide form (P₂O₅ and K₂O). That is how fertilizer labels usually report them. The amount of pure phosphorus and pure potassium is lower than 50% and 30%. The full guide linked above shows how to convert the figures.
2. Source material. The source material is given as monopotassium phosphate (MKP). MKP is a single salt that contains both phosphorus and potassium.
3. What Grotek says it does. According to Grotek, Monster Bloom helps the plant in four ways while buds develop:
- it supports the plant in building protein and starch
- it makes stalks and stems stronger
- it helps move sugars and starches around the plant
- it supports respiration and CO₂ uptake
Grotek gives these as product descriptions. The original article does not test them.
4. Dose. Use 1 teaspoon per 5 US gallons of water (6 g per 19 L). This is the same dose for soil, soilless media and water culture, which means roots growing directly in nutrient solution. Add it every time you fertilize during flowering.
5. When to use it. Start when buds begin to form. Stop 1–2 weeks before harvest.
6. Growing systems. The directions cover soil, soilless media such as peat and coco coir, and water culture (hydroponics).
7. Pack sizes. It comes in 130 g, 500 g, 2.5 kg, 5 kg and 10 kg packs.
Translator’s note: a teaspoon of powder is not an exact measure. How much fits depends on the spoon and on how tightly the powder packs. Weigh it on a digital scale that reads to 0.1 g. That way you give the same dose every time. Here is the label dose scaled to common tank sizes:
| Water volume | Monster Bloom (label dose) |
|---|---|
| 1 L | about 0.32 g |
| 19 L (5 US gallons) | 6 g |
| 100 L | about 32 g |
Grotek does not explain why it tells you to stop 1–2 weeks before harvest. Growers disagree about what the last weeks of feeding should look like. For that discussion, see Pre-Harvest Flushing: Science or Myth?. Mark the stop date on your grow calendar when you start using the product. Then you will not miss it.
Before You Add It to Your Feed
It is a supplement, not a complete feed. Your base nutrient still has to supply nitrogen, calcium, magnesium and the micronutrients. If you swap part of your base nutrient for Monster Bloom, the plant will run short of these elements. Keep feeding the full dose of base nutrient that its label gives for flowering, and add Monster Bloom on top.
Check EC and pH after you add it. EC (electrical conductivity) shows how much dissolved fertilizer salt is in the water. pH shows how acidic or alkaline the solution is. For how to measure both, see pH & EC: The Nutritional Foundation Every Grower Needs to Know. Measure the final solution after Monster Bloom has fully dissolved, so you know what is actually reaching the roots. Too much phosphorus and potassium raises the EC around the roots, and this can burn the leaf tips. For how to recognise that damage, see Nutrient Burn on Cannabis.
Do not stack two PK boosters. Your base nutrient line may already include its own bloom booster. If you add Monster Bloom as well without reading both labels, you can end up giving twice the phosphorus and potassium. Compare the NPK figures on both labels first. Then decide whether to use one of them or reduce both.
Test it on a small batch first. Put Monster Bloom on a few plants or one table. Keep a similar group on base nutrient only. At harvest, compare the dry weight and the condition of the leaves. That will tell you whether the product adds anything in your room, with your genetics and your base nutrient.
Translator’s Note: Using It Under Thai and Southeast Asian Conditions
Measure your source water first. Tap water, well water and rainwater differ from one area to another. Some sources already have a high EC before you add any fertilizer. Write down the EC of your plain water. Then you know how much of the final reading comes from fertilizer and how much comes from the water.
Watch the root zone in hot weather. At 30–35 °C, plants drink more and water evaporates faster from coco and peat. Salts left behind can build up in the pot over time. Check the EC of the runoff (the water that drains out of the bottom of the pot) once a week. If it keeps rising, the root zone is getting saltier than your feed.
Mix in the right order. Fill the tank with the full amount of water first. Add each product separately and stir between them. Never mix Monster Bloom directly with concentrated calcium products. Phosphate and calcium can react in strong concentrates and form a solid that the plant cannot use. Check the pH last, once everything has dissolved.
Store it dry, especially in the rainy season. Seal the bag tightly after each use and keep it in a dry place. Damp powder clumps, and then weighing becomes less accurate. Small home growers will finish a 130 g or 500 g pack before it gets the chance to absorb moisture. Larger packs only make sense if you use them up quickly.
Where to Buy and Which Documents to Ask For
Buy from Grotek’s official distributor in Thailand, in the manufacturer’s original sealed packaging. This lowers the risk of counterfeit, repacked or old product. Ask the seller for two documents:
- the certificate of analysis (COA), which is a lab report showing what the batch contains
- the safety data sheet (SDS), the manufacturer’s document on safe handling, storage and first aid
If you are unsure whether a fertilizer is legally on sale in Thailand, see Verifying a Fertiliser Is Legally in Thailand. If your farm is working toward GACP (Good Agricultural and Collection Practice, the standard for certified cultivation), keep the COA and SDS of every input with your farm records. Then you can show what you applied, and where it came from, if anyone asks. Ask the distributor whether they offer technical support on feeding schedules. For independent experience, ask other growers in the General Nutrients Q&A section.
What to Do Next
- Measure and write down the EC and pH of your plain source water.
- Read the NPK figures on your base nutrient and on any booster you already use. This tells you whether you would be doubling the P and K.
- Weigh 6 g per 19 L, about 0.32 g per litre. Do not measure by teaspoon.
- Measure the EC and pH of the final solution after adding Monster Bloom, and record the readings.
- Mark the stop date, 1–2 weeks before your planned harvest, on your calendar.
- Run it first on a few plants beside a group without it, and compare at harvest.
If you have used Monster Bloom in Thai heat or in the rainy season, post your EC readings and results below this topic. You can also ask your questions here.