Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Flourite works just fine for years.
So do your dinner plates.
You just need to keep putting fresh food on the plates.
You just need to keep adding fertilizers to the aquarium.
Plants need about a dozen elements to grow. Some are easy to get (hydrogen, oxygen). Some are supplied in fish food, or the water. Some are in short supply, and are the first ones I would look into supplementing.
Fish food supplies quite a bit of N, P and most trace minerals.
Fish food is low in potassium, iron, and calcium (and perhaps magnesium).
Fish supply some CO2, and some CO2 enters the water from the air. These sources plus decomposing plant matter can supply enough CO2 for a low tech tank.
Water with a GH of at least 3 German degrees of hardness usually supplies enough Ca and Mg. When in doubt you could add some GH booster like Seachem Equilibrium. You are looking for a balance of Ca:Mg of about 4 parts Ca: 1 part Mg.
If you know your tap water is low in just one of these minerals you could supplement just that one. Calcium chloride for calcium, Epsom salt for magnesium.
Potassium and iron are the two fertilizers that I needed to supplement even in a low tech tank. Use a chelated iron.
I would also supplement carbon. Excel is a good product, DIY yeast/sugar method works. Pressurized CO2 is best. One sign of low carbon is that the bicarbonate users (Valisneria) and slow growers (Crypts) are OK, but faster growing plants are not. They need more carbon that is entering the water in a form they can use.
Part of the key to this is regular supplements. A substrate with high cationic exchange capacity can even out the supply by holding on to many of the fertilizers until the plants need them. But if the plants have used them all, then the reserve is gone.
If you can follow the estimative index method for several months this will recharge the substrate.
Read the label on substrate tablets, and add these near the heaviest feeders. Whatever these tablets lack will need to be supplied in some other fashion.