Thanks for answering. The leaves veins are still green but the rest of the leaf is pale green, and goes towards yellow. In fact, in the same closet under the same conditions, some plants seems healthy and some are yellowish, some are yellow in more little buckets some are green in big buckets. I add CO2 with yiest and sugar, fans running, etc. The PH must be good because the soil is PH 6 and the water is PH 7 and some plants are OK. What does the description of the leaves make you think about ?
Thanks
Fhydro