I haven't done hydro in a while, but I'm going to take a shot at this.
In my experience leaf curl usually mean one of two things - either it's too warm in the grow space, and at 84F this might be it for an indoor grow, or the seed's genetics are kind of old. I've seen old seeds produce funky shaped leaves. Usually the leaf curl is a process called transpiration and it's a result of air temp being too warm. The leaf is trying to shed heat or retain water, not sure which right now. It could be pH, but my bet is on your temp. I don't think the cloth in water thing will help. You'll probably see a good change if you can bring the air temp down below 80F. It looks a little pale green and if anything it's time to give some ferts. I'm going to suggest what I usually do and that is to try Dynagrow 7-9-5 from your hydro shop. It's a one-part fert so you only spend money on one bottle, unlike many others where you need to buy two or three. The problem with Dynagrow is that it has both calcium and phosphorus in the same container and these compounds have a chemical attraction to each other. They bind together and sink to the bottom of the container over time, which means that this fert doesn't have a long shelf life. You can't let it sit around for a year and expect it to still be good. When you buy more than one bottle of ferts to mix together, like the GH products, you get the flexibility of adjusting how much to use of each part and you get longer shelf life. However, Dynagrow is a good fert and since you're growing in hydro, would be a good one to use. Last I recall, the directions read to use one teaspoon per gallon for a hydro grow. It's much less for soil but it's good there too. It has most or all of what plants need to grow, even cal and mg, so you won't need to add any. I've used distilled before with great results in a hydro grow and Dynagrow fert. I don't think plant death is in the cards if you try distilled. I don't understand why you're giving so much Superthrive. Follow the directions on the containers of stuff you buy. Supernatural has also been a great fert for me. You would buy the "Aqua" version and follow directions. It has pretty much everything plants need too. It's a crystal form and can be kind of strong so be careful how much you use. In any case, it's interesting that your plant was able to grow that big without fert so far. Time for some juice. In hydro, it's smart to get a ppm meter and shoot for a ppm level of about 900 for a plant that size. Usually you take it up to about 1100-1200 as the plant grows. Mix your fert in water first, check pH and ppm, and if ppm seems good but pH isn't to your liking, then adjust it. But I think the hydro range is actually pretty wide. Some people say 5.5-5.8 but I grew a plant in DWC to about 6 feet and never checked pH because I was too cheap to buy a meter. I just let it fluctuate however it wanted, trusting the fert company to do me right. It worked.