The Marsilea hirsuta has been a wonderful carpeting plant, but it first went into the Fireplace Aquarium nearly 27 months ago and has started to become problematic. Over long periods of time the marsilea can build up into a mass, I think as newer individual stems try to outgrow the existing carpet layer, so there had been a gradual creeping upwards. Since the marsilea grows as single leaves at the end of a stem it can’t really be trimmed effectively. It is possible to pull out interconnected strands as the plant propagates using runners, however, that tends to drag up surrounding marsilea where it is impossible for the uprooted material to be effectively put back down on the surface. Still, two-plus years is a good run!
Removing aquarium plants can make a huge, but temporary, mess
(Pro tip: don’t worry about it)
Pulling up the marsilea also released a huge pile of floating debris of all sizes. Part of what might be happening here is that debris becomes trapped between the layer of carpet leaves and the substrate, being very difficult to remove whilst the carpeting plant is in place. In my experience, even though so much rubbish suspended in the water column looks dramatic, it does not adversely affect any of the animal life, and indeed the fish, shrimp and snails seemed quite unperturbed. I followed the uprooting with a large water change (80%+) which cleared quite a bit of suspended debris out, but even so things were pretty opaque. Not to worry and no special measures needed though, the fine debris inevitably clears itself in a day or two.
Looking for replacement (aquarium) carpet
I’m going to let things settle for a bit and then probably put in some new carpeting plants where the marsilea was. One consideration is that since the carpet will be inconveniently behind and underneath the mountain, regular trimming will be difficult or impossible. That means some of the fast-growing carpets that need regular trimming to stay nice such as dwarf hairgrass (Eleocharis parvula) or Monte carlo (Micranthemum tweediei ‘Monte Carlo’) would not be good choices. I’m also shy about plants that can get very leggy under lower light conditions. One possibility would be to simply replant some fresh Marsilea hirsuta, or its smaller relative Marsilea crenata. I’m also toying with giving Littorella uniflora another try, where the compare/contrast between growth under low tech (no injected CO2 gas) and high tech (with injected CO2 gas) conditions might be interesting.