Yellowish cryptocorine leaves

[Turin Turambar]

I probably have Crypt. cordata (blassii), and I noticed that older leaves have yellowish edges. New leaves are always more green than older ones. I also noticed that I never had more than 7 leaves. The plant constantly put new shots, but if the plant has 6 or 7 leaves, one turns yellow and I need to cut it.

The leaves float on the surface, so they are under some high lighting. Could that be the cause (I've read somewhere that Crypts don't like much light)? I use both liquid and tablet fertilizer, CO2 and all other plants flourish. thanks.

[djlen]

My experience is that Crypts. do well in low light and better with more.
Sounds more like a nutrient deficiency(N or Fe?), but can't be sure without knowing exactly what you're dosing and what your lighting is.
Also, what do you mean, "...plants float on the surface...." ?
What is the tank size?

[Turin Turambar]

Hm, yes, nutrient defieciency, I thought of that too, but it's unlikely, or maybe Crypts are highly demanding plants.

N level (nitrate) is 5-10mg/l and Fe level is 0,25 - 0,5mg/l. So they are good. However, it is true that the red side of the new leaves are deeper in colour since I provided them tablet fertilizer (I started adding that 1,5 months ago). Maybe they will not fade so fast?

The tank is 60x35x35cm. Lighting is 2x15w Sylvania Grolux & Phillips Aquarelle tubes with reflectors.