I have two ten gallon tanks. One is generally choked with
Vallesneria, in the other one I can not get Vals to grow at all, the
roots die off.

Same lights, same water (Hard tap water) same substrate (pottery clay
beneath commercial aquarium gravel).

The only difference that I can identify is that in the one without
Vals I have a form of string algae growing.
--
Charles

Does not play well with others.