Clay substrate is the popular choice for riparium planters, it works well in tanks with a background where the clay gets hidden by the foliage and blends into the background.
But my tank is free standing, "front" and "back" are relative to what side of the desk you're on. Clay, gravel, or any other colored substrate would be very obvious, distracting, and would block light. So I started going over options for light or clear substrate.
After doing some research, it looks like the ideal riparium substrates are:
- Have enough gaps for water / air flow
- Not too heavy for the planter
- Not too light to float away
- Big enough not to spill out of the planter holes
Options I considered were:
Option 1) Filter sponges or floss. Since a lot of "ripariums" are planted HOB filters, we already know these work really well as planting medium. They're light colored and not super distracting, but they're opaque and would still create shade.
Option 2) Glass beads. I think these are too heavy for planters. Maybe okay with mine, which have hooks, but definitely sounds like a bad idea for planters with suction cups.
Option 3) Plastic beads. They would be lightweight compared to the glass beads. Some might be TOO lightweight and float. All the ones I found were too small and would have spilled out of the holes in the planter. This seems like the ideal clear substrate, if you can find the right thing.
Option 4) Floral water beads. This is what I ended up using.
Floral water beads are a water absorbent polymer. They are non-toxic and biodegradable. The gel is used to give drinking water to insects. But are they safe for fish?
Answers were divided. No one seemed to have any evidence, anecdotal or otherwise, if these are aquarium safe. I erred on the side of "Let's experiment!" and tried them out.
Here's what I found:
- You need way less beads than you think you will.
- The clear water beads are invisible in the water.
- They are lightweight. They will not float, but if the planter is SLIGHTLY uneven, they will absolutely spill out. I had to add extra plastic to the hooks to get my planters to stay level, to keep them from falling out.
- I'm not sure, but they might come out if the planter is on suction cups and completely underwater. Maybe they could be capped with glass beads?
- In retrospect, it might be a good idea to use a lightly colored (yellow maybe?) bead, because groping around the bottom of your tank for literally invisible beads is a pain in the butt. They are also kind of slippery so it's hard to pick them up.
- I'd worry about the possibility of fish eating them. Fortunately, the fish don't have access to the inside of my planters. Unfortunately some of them spilled out into the tank, and I can't see them, so I'm not 100% sure I got them all.
They will eventually degrade, but it's easy enough to pop the hanging planters out and replace them.
So far there have been no ill effects in my tank to plants, fish, or inverts.
Here's some pics:
You can see the planters, and the plant roots, but not the water beads:
From the "back" (the black blob is lady zebra nerite snail):
The beads are visible from the top (these are above the waterline):