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.
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".
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.
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.
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.
A week after that, my first harvest.
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.
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