You can mix tap woth RO to remineralize the RO water. How much? Depends on the tap water ph, gh, kh and what water parameters you want for your aquarium. You can also remineralize with baking soda and something like GLA GH booster.
You also have too much light. Try cutting to two bulbs with the others for a quick noon burst for an hour or so, but no more. At 1 bps is your drop checker lime green? If not, maybe increase your CO2. I have a 55 gallon and run 4-5 bps. I also only have a 3 bulb fixture. So i run less light and more CO2, and no algae. If your tank is still really bad, maybe it would be easier to empty it and clean your plants with an H2O2 dip. You can then add proper water with clean filters and a better understanding of your initial mistake. Another thought is the "One Two Punch" Algae treatment discussed and explained on this forum under the Algae thread. You first add H2O2 to entire tank folled by Seachem Excel. I havent tried but it appears to work great for entire tank treatments. Can be hard on some fish and inverts though. Also would recommend dosing Seachem Excel daily. Excel is proven to help control most types of algae.
Not familiar with your ferts. I use dry ferts purchased from GLA. Macros/micros dosed every other day, alternate days. EI Dosing.
Finally, are you doing regular water changes? Good tank hygein is always helpful. I change 50% weekly, sometimes even more. This is required for EI dosing, but also helpful regardless.