I have grown in
Promix for decades. It is almost impossible to mess up unless you overfeed things and start messing with the Ph.
Promix is buffered to keep a Ph of between 6 and 7. Why are you using RO water... is your local water that bad? Tap water usually provides minerals that avoids the need for additives like
Cal-Mag.
Promix (if it is the baled product, not their general purpose potting soil which is different and loaded with nutrients) will hold enough water to keep the root zone damp but still allows Oxygen into the roots. When I start seedlings directly into a 5 gallon bucket, I water about 2 inches around the seedlings area, about 8 oz, twice a week. It is important to thouroughly soak the
Promix well before planting to activate the buffers, etc. As your seedling grows new roots, it will spread out into the already damp areas and shouldn't need much water for the first 2 weeks. Slowly increase the water as the plant grows bigger. After a month, I usually water every 2-3 days and at 6 weeks it is every other day. Some strains use more water... it seems Sativa takes more in my experience.
I feed a general purpose 20-20-20 fertilizer (Jacks) about every 12-15 days after 4 weeks. If you follow that schedule, you should avoid deficiencies, lockouts, Ph issues, and most other problems. You might need to supplement the feedings with a light snack. I usually mix about 20% compost/manure into the
Promix, along with a handfull of sustained release fertilizer (Osmokote). This provides a lot of micro and macro nutrients and keeps a little nutrition in the
Promix between feedings. Since you haven't added this, you might need to find a light nutrient to go between feedings.
I know a lot of information is confusing. I have used this basic recipe for over 30 years and it is almost foolproof. Patience and restraint are the most important factors other than light and medium. At least in my opinion.
