Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Fish food contains a fair amount of:
N, P, most traces.
Fish food is low in:
K, Fe, Ca, Mg.
Fish eat the food. They excrete most of the elements in their waste. They excrete N via the gills, as ammonia.
Bacteria and other microorganisms can also digest fish food. If you had no fish, no shrimp, no snails in the system, just microorganisms you could use fish food as (very expensive) fertilizer, but would need to supplement the things fish food has in short supply.
Water changes with water that has a GH of at least 3 German degrees of hardness will supply the Ca and Mg that fish and plants need. If your tap water is very soft (very low GH) then you can use a GH booster like Seachem Equilibrium to add Ca, Mg, K and a small amount of Fe. I am not sure if it supplies enough K and Fe, unless you add way more than you should- the Ca and Mg would be too high for soft water fish.
You should find sources for K and Fe. One example that is reasonably priced on a small scale is Seachem Flourish Potassium and Seachem Flourish Iron.
Bettas might be one of the Anabantoids that actually need to breath air. They cannot get all the O2 they need via gills. No matter how well aerated the water is by trickling though the gravel bed, they can drown in water that does not have a fresh air pocket for them to breath in.
I would separate the planted sump and the tank so that there is such a space at the top.
I would also add plants, driftwood or something to the tank so the Betta has a place to rest (they often like to lie on the leaves of tall plants) and a place to hide.