The theory by other sounds good, but is only a theory. (Not saying I know anything)I fertilize by substrate only with tabs. Lights are 330watts over a 125gal that are on for 9 hours a day with C02 injection.
This is what concerns me, fert tabs only with high lighting. It may be the cause, but also just another theory. Maybe too low N?
I just received some red tiger lotus, it was not really that red when I got it, mostly green w/ red specs. The only new leaf that is growing is brownish color. I have Lower lighting(~2wpg of ODNO T8's). Also I had low nitrates b/c I have no fish and did not dose enough to start(which also accounts for my algae issues at this time, again I'm new at this stuff but love to learn)