It just really depends, with a tank that small and slow growing plants
you just have to see how things go with the amount of light being used.
Light is the main factor, that determines what is needed.
Adding a little K, and Comprehensive a couple times a month may suffice
while allowing the betta and it's food to supply the other nutrients in
small amounts is usually good enough.
A 15w fixture seems like it would be a bit on the high side but once again
it depends entirely on the lighting/bulb/reflector/intensity.
If it is on the high/er side of light, then adding a touch of all nutrients ie
N,P,K, Comprehensive, Excel once a week will improve things.
Without actually seeing your setup and the plants in response to there
current situation, you just have to get a feel for what is needed.
If you do dose all nutrients, without the addition of C02, it will not take
much of each nutrient, so only small amounts.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.