. I contacted the seller I bought the light from and he claimed I need to keep the light 24" to 36" MINIMUM from the light. I've raised it to about 33" from tops and bleaching has stopped.
I have the same problem with two strains, I got two "old style" 300W MarsHydro (60x5W LEDs) and the seedlings are very yellow, almost white! I already moved the light at approx 24" distance now.
I am wondering whether after you moved the light 33" and as you say the bleaching stopped, did you move the light down again once the plants were bigger? Because otherwise 33" distance sounds like awfully far away for me. I am so confused seeing those two plants yellow/white at 24" distance while others say they don't have a problem growing with their LEDs a lot closer, like 18".
Sidenote: While I love the MarsHydros (nice price, €100 each shipped express) they have an annoyance...this is that after a few days in my greenhouse (on the balcony) and very well vented, in AWFUL Spanish heat, right now 100F (38C-40C) at noon they always get a smeary "film" inside on the glass after some days. I already opened the lights two or three times and cleaned the film/glass, but it seems that some sort of oil from the thermal paste or whatever is "sweating out" from the PCB under a lot of heat and creating this film. (One lamp I opened had one of the drivers (?) all oily). I don't want to entirely remove the glass since I want to keep the LEDs somewhat protected from water etc. Just wondering whether someone experiences the same with that film on the glass.