cant be co2, i have a pressurized co2 at 2 bubble/sec in a 15 gallon biocube. The dropchecker is almost yellowish. I remember reading a while back this could be one of the macro deficiencies, but cant find the thread anymore.With my limited experience, sounds like not enough CO2 possibly. Although Vals are pretty easy to grow anywhere. Would help to know more about your tank. I recently had a CO2 issue that had been going on for close to a month before I figured out what was going on. I put some Rotala Indica in my tank and the stems never straightened out from the way they droop a little when you first put them in there. Fixed my CO2 issue and within a few days those stems were as straight as a nail. The CO2 issue didn't affect the other plants I had in my tank, but I did get a bad bout of BBA.