Undergravel UAS

I have a small, 21 gallon tank I made from a larger broken tank. For filtration I'm using an under gravel filter with lava rock for biological and mechanical filtration.

Attachment 6060

Instead of using tubes to pull water from under the gravel, I made some fiberglass boxes. I used a 2x4 for a mold, so it measure 3.5" x 1.5".

Attachment 6061

Then I added 660 red, 3w, leds, and covered them with more fiberglass resin for waterproofing. There's a pair of boxes, one has 5 lights in it, the other has 10. The one with 10 I have attached to a dimmer.

Attachment 6062
Attachment 6063

Here it is installed in the tank. There's a big nursery housing some fry that blocks the view other one, so there's no picture.

Attachment 6064

I tried using string to for the algae to grow on, it didn't work. The string got all tangled up and disintegrated. So I replaced it with some of the black knitting mesh that was roughed up.

I was paranoid about how hot the led's got in such a small tank. I didn't want to overheat the water and kill the fish. So I started off with 1 box light with 5 lights only. The box seemed to be a total bust. There was black algae all over the glass but the inside of the box was pretty much completely void of anything.

With no appreciable change in water temperature I then added the second 10 led box with the dimmer turned almost off, ~10% output. Now I can do head to head comparisons at the same time. I didn't keep a good log of the time frame, but around 4 weeks later... the box with 5 lights running at 100% had some promise.

Attachment 6065

A week after that, my first harvest.

Attachment 6066
Attachment 6067

Not a ton of growth, but I have a pretty large dual screens and only 5 small fish and a couple of fry. The entire screen is green, there just isn't much that's long enough to pull off.

I was a bit surprised at how much red light came through the fiberglass. With no light coming from it, you certainly can't see though it. The light spilling out has a lot of growth on the tank. My plan is to coat it with something to trap the light and make it less of an eyesore in the tank. I didn't want to get that involved in it until I knew that it would actually grow algae. So now that I know it works, I'll have to do some more refinement. I also turned up the box with 10 led's from 10% to 100% output, I'll have to wait and see if 15W or 30W of light grows more algae.

So far, I'm very pleased. I have a small tank that is completely free from anything hanging off the sides or top. Once I get the algae scrubbers disguised better I will have a very clean natural looking tank. Instead of a mess of plumbing and equipment, in the tank or hidden in a sump, that I really don't want.

Very nice. You could tuck it away in a fake rock or stump.

Strings are not as good in FW, as you saw.

When the tank is done where is the scrubber going to be?

It will be in the back corners of the tank. I made them with slip on pvc fittings so I can just slide them out to clean them. I still need to route the air line into the base instead of the scrubber so it's easier to remove.

If I understand correctly you are running a ugf with the scrubbers providing the flow through the filter? Is there any way you can coat the box that holds the scrubber white to reflect the light back and to keep it from the rest of the tank?

Here's a picture of them installed on the tank with lid off.

Attachment 6080

Update, I ran both uas at 100% power. One with 5 lights for 15 watts, the other with 10 lights for 30 watts.


Attachment 6081

30 watts must be too much light, there is very little growth and a lot of it is pure white. The 15 watts is growing well, but to be fair it was much better established. Though, the bulk of the grown is away from the lights. I'm not sure if that's because there is too much light, or not enough air on the other side?

Attachment 6082

I guess I'll turn the 30 watt side down to 50% and see how it looks next week.

Great thing about being dimmable is you can dial the light in just right.

Well after two weeks I took my scrubbers out.

The 15 watt is slowly going in.
Attachment 6158Attachment 6159

The 30 watt is working better turned down to ~50% output. The algae is green instead of white now.
Attachment 6160Attachment 6161

Neither one is very thick. I was thinking that I over sized the amount of screen area I need, and would need to make it smaller. Two things come to mind for me.

The first is that due to the "transparency" of fiberglass there is quiet a bit of green algae growing on the glass and gravel near the boxes. It's not growing very fast, but is apparently finding enough light and nutrient to at least sustain itself. I'm sure the scrubber would grow better if no light escaped. So I'm trying a black 2 part epoxy that I'm using to coat the outside, hopefully that will trap the light and kill off the surrounding algae.

The second thing that comes to mind is so what? Right now there is enough screen area for the algae to spread out and grow slowly, and it appears to be healthy green algae. At the current rate of growth, I estimate that I would only have to clean out the scrubbers about every 3-4 weeks.

Here's the tetra easy test strip results.
Attachment 6162Attachment 6163

The results speak for them self. I should note that in the last 4 weeks, I've done two water changes of ~4 gallons each. The last one was over a week ago. Probably next weekend I'll add the fry to the main tank and clean the algae off the glass and gravel.

Until the next update.

I think the screen will fill in after you scrape it all off down to the white.

Thanks for the suggestion, easy enough to test I guess.