Eh, it's a water change. I don't really
enjoy it, but I do like the look of a nice clean tank after all the rocks have been blown down and the sandbed is clean. There's always a little cyano somewhere in a seahorse system, no such thing in my house as a ULN tank unfortunately.
I do a 5-10g water change every weekend, with occasional skips. The skipped weekend is always followed up by a 10g change the following Saturday, though.