Hi, I went ahead and built the horizontal scrubber as planned. Now it has been up and running for over 2 months. It seems to be effective.
I have 2 x 100 gal mbuna tanks with approx the same number/size fish (30 or so).
For one tank
I have built a 150cm long 12cm wide 5cm deep tray out of black forex (expanded pvc) glued with Tangit and sealed with black Dow Corning 881 silicone.
It sits on top of the tank braces. Water comes in one end courtesy of the return from one of the (Jebao 304 nominal 1200 l/h) canister filters, flows over the Darice #7 roughed up canvas and falls back in the tank by means of a height adjustable overflow. Lighting is by 4 of the red/blue 8w LED strips that are on 14 hours overnight.
The plastic canvas is partially covered by green hair algae, I have on purpose not done any water changes in this tank for 4 weeks and the nitrates (Sera liquid test kit) have remained barely above 5mg/l. In the mean time on the 1st May by means of two massive water changes I dropped the nitrate level in the "unscrubbed" tank to below 5mg/l.
These are the latest results (colours in the picture appear darker than they are in reality) the scrubbed tank after one month without water changes is still under 10 mg/l while the unscrubbed one after 18 days has climbed to close to 25mg/l
I will give the scrubber a little longer to mature fully then I will bring the nitrates in both tanks to close to zero and repeat the test, possibly monitoring for phosphates and desolved oxygen as well as nitrates. Ciao to all