I don't understand the difference between RO water and dionized. I thought RO water with about 20ppm is essentially dionized. If you've been using it this entire grow, I don't think it's the water. If you got through veg without feeding, that means the soil had a lot of nutrients (I'm surprised the seedlings didn't burn). You could have started feeding, but transplanting into more soil complicates things I think. The plant should have access to fresh nutes in that new soil (if it's the same soil that had enough nutes to carry the plant through veg). I would continue feeding water and see how it goes because it looks like burn from overfeeding. Or, very mild nutes (maybe 1/4 what you fed?). I'm not the right person to direct you because I haven't used FF.
I mix 50-60% Pro-Mix HP+Myco, 20-25% Kellogg Patio Plus (potting mix), 20-25% Perlite. (Somewhere between those percentages). I amend 1 to 1.5Tbsp (per gallon of soil) Fertilome Hy-Yeild Agricultural Lime (dolomite). I wet it 2-5 days before using.
I feed Grow More Sea Grow (All Purpose and Flower & Bloom), and some Potassium Sulfate (K2SO4) bought from Alpha International Chemicals on Amazon or eBay. Also AK Fish to boost N in veg, and AK Kelp as a flower hardener late in flower.
And, 5ml/gal Botanicare Liquid Karma to help the soil microbes. (I use that every feeding, but maybe only 1ml/gal at the end of the first week, 2ml/gal the second week, then work my way up to 5ml.). I add a pinch (1/16th tsp/gal) sugar to help feed the soil microbes. Sometimes a 1/8tsp molasses. It should be all the same. It's just carbs feeding the microbes. Molasses has minerals and sulfur, so I use that occasionally instead of sugar.
I mix those things to get an NPK ratio in veg between 1.2-1-1.7 and 1.8-1-1.7. I walk it up and down depending on what the plants look like. For example, in mid veg I might feed 1.8g AP, 5ml AK Fish, 5ml Karma and 0.45g K2SO4. That's 1.58 - 1 - 1.71.
In mid flower, I mix 1.5g AP and .80g F&B (plus 5ml Karma) to get 1-1.64-1.71.
At the end, 1.1g and 1.1g (plus 5ml Karma) for 1-2.1-2.1. Add 5ml Kelp as a hardener (seems to me. I don't use it in veg because Sea Grow already has kelp. Supplementing seems to cause stretch due to too much auxins.).
If I get N def in flower, I revert back to more AP and/or Fish. I use
this spreadsheet to play with the ratios, "reading the plant" and adjusting things. I like Sea Grow because it's a balance of synthetic nutes for immediate availability and organic ingredients which are healthier for the soil. I used to grow with GH Flora 3-part (all synthetic). Myself and friends noticed a very distinct taste difference when I switched. It's smoother, richer (not as sharp, bright -- which I associate with harshness.). It's inexpensive.
But, what I really like is monitoring my own NPK ratios instead of following a schedule which obscures that info. When you see how the plants respond to different ratios, you can use any product(s) to get there. I'm growing a plant now with
nothing but MiracleGro Tomato. I'm going to follow that with one that mixes 2-3 MiracleGro products to get the ratios I like. (Not that I like MiracleGro. Just because I think it doesn't matter what's used. I want to try it.).
Your plant looks very good. I'm sure it will finish ok. 3-4 weeks left?
If you want to do something where the soil contains all the nutes (you feed nothing except some teas), check out @uwine99 's
no-cook soil. I'd like to try that sometime. I'd like to do more organic, but typically you have to let the soil cook for a few months. I'm not that motivated. But, what he describes sounds reasonable.
Also, for water, I start with 150ppm. I mix my tap water with RO water to get that.
