Dying rotala macandra - help please?

Hello. Hopefully you can help. I'm growing rotala macandra in my tank, which is doing pretty well, but the lower leaves gradually die. Is this generally a lack of a specific nutrient, Co2, or is it from having the light blocked?

The Co2 levels are good. In fact, a couple weeks ago I moved the Rhinox 5000 directly behind where they're growing and placed a spraybar above it, aimed slightly downward. I'll be honest by saying that I don't dose every day, but I feed the fish WELL once per day. Other than that, I do the usual EI dosing and do 50-60% wc's about every 4-5 days.

If you notice in the picture, the tops are doing quite well, but the bottom isn't so great. Could it simply be that as they grow, they shade the lower portions of the plant? If that's the case, how do people get nice bushes of this plant to grow without dying off?

By the way, the lights are Tek T5 HO, running 4x54w for 12 hrs w/ all 6 on for about 3 hrs/day. It's a 90g tank.
Any ideas? Sorry for writing a book. I wanted to give you all the info up front.

r. macandra (w/o flash)


r.macandra (w/ flash)


Thanks.

-Ryan Ingram

 

I'm guessing it's either the light shading thing, or still not enough Co2 actually getting to it. I don't see how the current diffuser could produce any more than it already is.
Maybe I should add a solenoid and buy a 2nd diffuser, so I can inject Co2 on opposite ends of the tank. I've seen some people do this to 4' long and bigger tanks with success.