I've got 2 C-99 about 4 weeks old that have started rapidly turning yellow on top and the upper leaves are curling upward. They are in soil with a decent amount of DTE amendment and are watered with RO water supplemented with Bloom City Cal/mag and Silica booster. Soil pH seems good (not the best pH meter) 6.8 - 7.1ish and I water with 6.8ph. They are under a 2ft 4 bulb T5 but currently only 2 bulbs are on. I turned 2 off at first thinking it was some kinda light burn or bleaching but I'm sure it's not anything to do with it. I've been reading through the plant problems thread for the last 3 days now and the best I can come up with is a sulphur deficiency because it's only on the upper new growth and it's about the only thing I haven't added amendments for. Let me know what you guys think it is and what's the best way to remedy it.