Sorry that I wasn't more specific. My substrate is a mixture of peat moss, a low-nitrate garden mix (cactus mix if I remember correctly) and sand, with a layer of sand on top. It totals about 4" thick.
I do use fertilizers in the water and fertilizer sticks from the hardware store for some of the plants, especially the lily and swords.
I was more curious about if the proper pattern would be to do several partial changes over time, or a complete change all at once. The later seems to be the consensus.
I am not having a problem with the growth of the plants (In fact, I have the opposite problem, if that's a problem. My LFS loves me.), but I don't like waiting for issues to develop before knowing what to do about it. My substrate is about 5 years old now, so it occurred to me that it might be getting tired.
Thank you all very much!
Mike