In October of 2022 I decided to make a Paludarium. A paludarium is like a mix between a terrarium and an aquarium. (The name comes from the latin word "palus", which means marsh.) I'm really into gardening and houseplants, and I've always been interested in getting an aquarium. When I learned about paludariums I knew I wanted to build one. I also was very interested in the idea of creating a somewhat stable ecosystem, minimizing the need to change the water and add food, with the main input just being light. I'm not a purist about this, but it is something I try to work towards.

Planning out the build

My plan for the paludarium was to have the water on the left third of the tank and the land on the right. On the back of the tank a waterway would flow on an overhang from the top right of the tank down to the left, where it would then turn into a waterfall into the water section, which would also provide aeration. In hindsight this was probably a bit too ambitious for a first build, but I really liked the idea of a complex waterway with a waterfall.

Choosing materials

After watching a handful of videos, I decided on building the backdrop from foam board insulation, coated with expanding foam, and then silicone and coconut fibers. I found a 29 gallon aquarium tank that I liked well enough (I do wish it was a bit taller). I bought a pump, tubing, terrarium dirt, aquarium gravel, silicone, expanding foam, coconut fibers, a misting system, sphagnum moss, leaf litter, some spider wood, lava rocks, sponge filter, substrate barrier, and a few other minor items.

Building the backdrop

The first step was to build the backdrop. I cut the foam board insulation to the size of the back of the tank, and then glued together the rough shape of the waterway. I then applied expanding foam to the foam board. This stuff is pretty amazing; it expands very quickly and hardens over a few hours, after which you can carve it with a knife.

Once I cut the expanding foam down to shape I was looking for, I coated the surface with silicone and pressed coconut fibers into it. I also created an opening and inserted a tube for the water supply to the top of the waterway, sealing it with more silicone.

Assembly

Once the silicone had cured and aired out, it was time to assemble. I rinsed the backdrop thoroughly and attached it to the inside of the tank with silicone on the glass. I split the base of the tank into two sections, separated by sponge filter. On the water side I laid down aquarium gravel, and on the land side I laid expanded clay up to slightly above water level (the false bottom), and then laid a substrate barrier (basically a piece of synthetic fabric) and then dirt on top. I placed lava rocks against the sponge filter on the water side, to improve the appearance and give a place for the future inhabitants to hide. I hooked up the pump system such that water flowed down the waterway and over the waterfall, and set up the misting system to spray mist into the tank a few times a day. I also placed a few pieces of spider wood, one in the water, and one that I placed in the soil, and glued to the backdrop.

Planting

I wanted to plant the tank fairly heavily such that nitrates would be readily pulled out of the water, reducing the need for water changes. For the plants I got two small Neoregelias, a Begonia ulmifolia, a Pellionia pulchra, a variety of Peperomia, and two other fern species that I can't identify. I largely chose these on a whim, just looking at what others seem to put in Paludariums. I attached the Neoregelias to the backdrop with toothpicks, and planted the rest in the soil. I also spread a live moss slurry over the backdrop. This starts off as just a brown goo, but eventually grows into a thicker blanket of moss. I also spread some leaf litter on the ground around the plants. I added springtails and some terrestrial isopods to the paludarium. These are the "Clean-up crew". They eat dead plant matter, mold, and generally keep the paludarium clean and healthy.

Adding shrimps and snails

Before adding aquatic animals, I needed to establish the bacteria that process the animal waste products. This is called cycling. I cycled the tank for about 10 days, which may have been a bit on the short side, but the bioload I was adding was pretty small, just ten Red cherry shrimp and a few ramshorn snails. I also added Salvinia, a floating plant, and Java Moss. I didn't really know what to do with the Java Moss, so I just threw it in the water. Most of it died after a few months, but the Java Moss that landed on various surfaces stayed alive, and now it's growing along a bunch of different surfaces underwater, and even out of the water a bit. After a month or so I noticed a different species of snail than what I put it, so it must have hitched a ride with some of the plants.

Maintenance

Every 4-6 weeks I do a ~20% water change with RO water with added minerals. I could probably go for longer (nitrate levels are always quite low), but I haven't tested it. I add food occasionally, but the shrimp and snails can also survive on biofilms which form on the underwater surfaces. Early on I was having some issues where the water was a bit to acidic (which wasn't great for the snails), but I've added a bunch of pieces of cuttlebone over time and Ph levels have gone up. I cut back the terrestial plants and clean out some of the Salvinia every month or so.

One year later

Almost a year later and I'm pretty happy with how the tank has grown in. The shrimp and snails breed and reproduce. It's fun to see the tiny shrimp whenever the eggs hatch. On the backdrop, different parts get different amounts of light and moisture, and this has led to different species of moss taking over in different areas. I really like the heterogeneity in that way. I'd still like it to grow a bit more, but I'm definitely happy with how far it's come. Unfortunately the isopods don't seem to have made it, but the springtail population is very strong. Especially at night if I turn on the lights, they are all over the place.