HeyPK, not quite true. I do not add under the roots: nitrogen, phosphorus and calcium. But once a week I sprayed anubias, solution of water with a complex fertilizer, in which the presence of: nitrogen, phosphorus and calcium. To do this, you can take any complex fertilizer for houseplants - 1 gram per 1 liter of water. And along with the plants live snails - Planorbis corneus var. rubra, they also produce nitrogen and phosphorus
Plus hard water - KH - 5; GH - 14, with such parameters, a lot of calcium.