This board is for questions about Grotek® fertilisers, a nutrient line from Canada. It covers how each product is used in a real feeding schedule, from transplant to harvest. Each product has its own thread. Two mixing mistakes come up often, so they are explained once below.
What to post in this board
- Questions about a Grotek product: what it does, how much to use and how to mix it.
- Feeding schedules that use Grotek products, for any part of the range.
- Questions not tied to Grotek, such as water quality, general pH problems or other brands, go in General Nutrients Q&A. That way the answer stays easy to find for the next grower with the same problem.
The products and where each one fits
Read the Grotek Fertilizer Guide: Feeding Schedule and Tips first. It covers the feeding schedule for the whole range. The table shows where each product sits between transplant and harvest.
| Product | What it is | Where it fits | Thread to read |
|---|---|---|---|
| Monster Bloom | A flowering booster: concentrated phosphorus and potassium with no nitrogen (Monster Bloom is 0-50-30) | Added on top of a complete base feed from the time buds form. Grotek’s directions say to stop 1–2 weeks before harvest | What a 0-50-30 PK Booster Does and How to Use It; Grotek Monster Bloom: Flowering Nutrition |
| Gro-Silic | A silicon supplement. It is strongly alkaline. | In the nutrient solution, or as a foliar spray from the 3–8 leaf stage and then once a month as needed (Grotek label) | Gro-Silic: Structure and Plant Strength from Root to Top |
| Vitamax Pro | Grotek describes it as an organic-based product with land and sea (kelp) inputs. Its thread describes it as a product for plant vigour and root development in early growth | Grotek’s directions: 1 ml per litre, once a week through the growing season | Vitamax Pro: Vigour and Root Development in Early Growth |
What to do: before each mix, note which growth week each group of plants is in. Then use the chart to see which products belong in that week. This keeps you from starting a booster too early or running it too long.
Flowering boosters go on top of a complete feed
A fertiliser label shows three numbers: the share of nitrogen (N), phosphorus (P) and potassium (K). On Monster Bloom, 0-50-30 means 0% nitrogen, 50% phosphate (P₂O₅) and 30% potash (K₂O). By label convention, phosphorus and potassium are given in these oxide forms, not as the pure elements.
With no nitrogen, a booster cannot feed a plant by itself. You add it to a base nutrient, which is a complete fertiliser that already supplies nitrogen, phosphorus, potassium and the other elements. Use the booster only during the window set in the feeding chart.
The boosters are very concentrated, so it is easy to use too much. If you run a booster for too long or at too high a dose, the buds do not get heavier. Instead, the leaf edges burn (nutrient burn).
What to do: start at the lowest dose on the label. Check the edges of the newest leaves every few days. If the edges turn brown and crisp, lower the booster dose or stop it, and keep feeding the base nutrient. The goal is to catch the problem while only a few leaves are damaged.
Translator’s note: in rooms or greenhouses running at 30–35 °C, heat and dry air can also brown leaf edges, and the damage can look the same. Before you change the dose, check your temperature records against the date the booster started. If the burn began on hot days and the feed had not changed, treat it as heat stress first.
Gro-Silic: mix order and when to check pH
Gro-Silic supplies silicon as sodium silicate (13% soluble silicon on the label). A silicate is a strong base, which means it is strongly alkaline. It raises the pH of the water, and pH shows how acidic or alkaline a solution is.
Grotek’s own instructions say Gro-Silic must never go into nutrient concentrate. Concentrate means fertiliser straight from the bottle, before you dilute it in the tank. Use this order:
- Fill the tank with the water you will use.
- Add Gro-Silic to the tank before any nutrient. If the water already has nutrient in it, pre-dilute Gro-Silic in a small amount of water first.
- Stir, measure the pH and adjust it to 5.5–6.5. Grotek says to do this before adding other nutrients, so that nutrients do not settle out of the solution.
- Add the base nutrient and any other products, then check the pH again.
Measure after the silicate is in because it raises the pH. A reading taken before you add it is no longer correct. If you adjust before adding the silicate, you will have to adjust a second time.
Translator’s note: tap water and well water in Thailand and Southeast Asia vary a lot in pH and hardness from one area to the next. Before your first mix, measure the pH and EC of your own water. EC (electrical conductivity) shows how much dissolved salt is in the water. Write both numbers down. Then you know how much of the pH rise comes from the silicate and how much comes from the water. The method in Irrigation Water for Living Soil works for any growing medium. If the final pH is too high, lower it with a pH-down product used as its label says.
Translator’s note: checking products sold in Thailand
The main law on fertilisers in Thailand is the Fertilizer Act B.E. 2518 (1975), amended by the Fertilizer Act (No. 2) B.E. 2550 (2007). Before you buy, check that the product is registered and has a Thai label. Verifying a Fertiliser Is Legally in Thailand shows how to check.
This forum does not recommend shops. To find a product, ask the official distributor in Thailand. You can also ask for other growers’ experience in Equipment and Supplies.
Ask your question below this topic
Post your question in a reply below. Include:
- the product and the dose
- your growing medium
- the pH and EC of your water
- the growth week
- a photo of the affected leaves
With these details, other growers can tell a booster problem from a water problem or a heat problem.
References
- Grotek product instructions and labels for Gro-Silic, Monster Bloom and Vitamax Pro, and Grotek’s official feeding chart. Product pages: Monster Bloom, Gro-Silic, Vitamax Pro.