Growing Plants Emersed On Top Of An Aquarium In An Acrylic Tray


Feb 3, 2017
I've seen examples of a small 2 or 3 gallon rimless tank with another small tank or an acrylic tray stacked on top that has plants in it. The plants are emersed. Actually the plants are in what I think are clay balls with water in the bottom. But I don't know how much water is in the bottom of the tray. Or do I need any soil? I want to try this, but I have a few questions.

I'll have the water pumped from the bottom into the top tray and drain back into the bottom tank so the water will circulate the plant roots.

Question 1: I have an acrylic tray that's 3 1/2" high I don't know how much water to keep in the bottom of the tray? I was thinking an 1"
Q 2; Can I use Clay balls or Aqua soil by them selves for the roots?
Q 3: Should I top of with gravel or just go with the clay balls or aqua soil?
I'll have a few Nano fish in the bottom tank with sand, lava rocks and small pieces of manzanita wood.
I would like to fertilize the plants a little if needed? Q 4: I don't know how much or how often to fertilize?

I haven't got the tray yet so I don't have any pictures.

I've watched a lot of videos but they don't explain the details involved in making these set ups.

If anyone out there has any details on how to do this, it would be very much appreciated.


Lifetime Member
Lifetime Member
Jun 3, 2013
The clay balls are a fired expanded clay, very porous like lava rock. I’ve used clay in a hydroponic veggie garden in a flood/drain setup and the balls do float until waterlogged. Not an issue if you have constant flow. You can also use pea gravel, rock wool, lava rock, etc, just something inert. Coco coir also works well, but not appropriate for fish unless you’re doing a black water biotope. Sand might be a little too fine but don’t see why it wouldn’t work either with proper screening to keep it out of the overflow. No need to use fancy substrates.

The premise is the water carries all the nutrients so no soil is needed other than to just anchor the plants and hold in the moisture for the roots. If you look at nft systems the water depth needed is minimal, less than 1/4 inch. you just need the plant roots to reach it ok and that you have a reasonable flow rate for nutrient transport. I’d aim for maybe an inch or Less. Then add more for the “dry” layer to fill in the depth you need so the top isn’t wet and anchors the plants well. I also used seedlings in net pots and rock wool, no substrate in the tray itself and water just high enough to touch the wool. Many ways to do it.

I think the simplest way would be a small pump running constantly from the tank to one end of the tray, and an overflow on the other side going back to the tank. Height of the overflow determines depth. I’m using essentially the same configuration with a timer and an extra hole drilled to accomplish a flood/drain cycle.

For ferts standard ei style is fine I would think. With atmospheric co2 available, it may take more than you’re used to. Something fish safe.

Keep us posted. :)