Diana Walstad says, in her book Ecology of the Planted Aquarium, that she overfeeds her fish a little to provide food for the plants. As explained, this decays into ammonia. If your tank is properly cycled, the ammonia will quickly be turned into nitrites and then nitrates. This will feed plants and algae. So, it has to be balanced with the proper amount of CO2 and light to avoid algae.
Supposedly, fertilizers like Seachem Flourish are designed to feed plants without encouraging algae. A 250ml bottle of Flourish costs about $6 and will last a long time.
Some plants need nutrients in the water and some need nutrients in the substrate. Anubias get their nutrients mostly from the water. Crypts need nutrients in the substrate. If they don't get them, they put roots up into the water.
I use both Flourish liquid and Flourish tabs. The tabs are pushed down into the substrate about every 4-6". The tabs are rather expensive at almost $1 per tab. Fertilizer tabs are available from other companies for much less $$.