Newbie planning a horizontal scrubber for FW tanks

Hi and Felice Anno Nuovo (how we say Happy New Year here in Italy). I have a 6' and a 5' mbuna tank, a 4' Southamerican planted, a 45g oranda and planning a 95g discus tank. All the tanks run on external canister filters that are doing their job ok - that is producing nitrates. I try to keep them at 25ppm by means of water changes. I am thinking of building a horizontal algae scrubber that would sit on top of the braces in my 6' mbuna tank
https://youtu.be/L68lihNMCkQ

I have about 2.5" between the braces and the (self built) hood. I was thinking of putting on top of the braces at the back of the tank some kind of shallow tray probably made with electrical trunking. Could manage 5' long by 5" wide. Can I have the plastic canvas lifted just 1/2" from the bottom of the tray? I would have a small pump in the tank pushing water up in the tray on one end and an overflow on the other end to return the water to the tank. What level should the water reach in the tray and what kind of flow (g/h)? I am thinking of using warm white and deep red LED bars (similar to those already in the hood, although at the moment for lighting just using cool white, warm white and blue). The video shows a good growth on the rocks in the tank, that built up from nothing in 3 months and with the mbuna constantly grazing on it so I hope the LEDs will be adequate.
I hope not to be getting ahead of myself but should the algae grow can I let the mbuna graze on the canvas when it comes to removing some of the growth? Can I grow Daphnia in the scrubber to simulate the aufwuchs?
Should it prove effective I would replicate it for the other tanks.
Thanks for any advice you can share

Welcome from Italy to the new year.

Why lift the screen up from the bottom? The screen needs to have a very thin fast-moving layer of water on it. Best way for yours is to put the screen on the bottom of it's pathway, and tilt one side of the pathway up as high as possible so the water flows like a rough river across the screen. You don't want water going below the screen, and you con't want more than 1/2 inch of water on the screen. 1/4" is best.

How would the fish be able to get to the screen to eat? If you mean putting the screen into the tank for this, you can but it will get messy as all the pieces let go and float around. Better is to scrape the screen and let a little go into the water by itself. This way you don't have to lift out the screen. You could however add a smaller, removable section of screen on top of the big screen, and you could remove this section to put into the tank for eating.

I don't think you can effectively grow anything in particular in/on the screen; it will just grow what it wants to, and the excess will flow down into the tank by itself. Scrubbers grow a lot of little animals that do this, and many times the fish learn to just wait around by the scrubber's drain to catch it.

For lighting, you could try to just use your display lights. If adding lights, try not to use whites if you can avoid it; use reds or grow-lights if they don't change your tank's lighting appearance.

Thanks your advice is really usefull. I am happy with the display lights for the tank but it is no problem at all to add specific ones for the scrubber, avoiding as much as possible the deep red leaking out of the scrubber (makes the display look not it's best). Still not clear if I should aim for a 2700-3000 K light or aim for the clorophyl A wavelengths of red and blue. Ciao

If you can't have reds, or reds+blues, then 2700k "warm" or "soft" would be best.

Hi Paul. Nice mbuna aquarium. I like your rock work. Is the purple color from the rocks, or an algae growing on them?

Hi Mark, Happy Nee Year. The colour is algae growing, the rocks are a naturally a very pale sandy colour (some kind of very hard sandstone). They come from the paddock just outside the door (no shortage of supply, and I like a "heavy" scape to keep the fish amused). They are starting to grow also on the rocks in my more recent 2nd mbuna tank. I hope that even if the algae scrubbers take off there will still be algae cover on the rocks for the mbuna to do their thing.
I am looking at these lights
http://m.ebay.co.uk/itm/WYZM-6-Pack-...%257Ciid%253A1
Any thoughts?
Ciao

Your going too need higher wattage led chips. It lacks the power to penatrate water.

Even just the 1/4" sheet of water, if that, that may be flowing over the plastic canvas? The strips woul be only about 1-1.5" from the surface of the water/plastic canvas. The tank lights are even crappier but no shortage of growth both on rocks and glass.

Yea those lights strips are very week. Looks for at least 15 watts for each foot of scrubber length. Preferably 30 watts.

Yes your rocks grow now, but not fast. A scrubber can growth that thickness in one day.

Thanks will do

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
http://i1108.photobucket.com/albums/...ps2ed5pxt9.jpg
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.
http://i1108.photobucket.com/albums/...psiwtdkyct.jpg
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.
http://i1108.photobucket.com/albums/...psysevpnz2.jpg

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.
http://i1108.photobucket.com/albums/...psr1xtnxjw.jpg

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
http://i1108.photobucket.com/albums/...psxwzju6cl.jpg

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

That's a long one. Seems to be working about right. When it gets thick the nitrate might be zero.

You are right, now almost 8 weeks since last wc and nitrates are down to 0. Did 50% wc anyway as needed to water the veggies, seems a waste to pour pristine tapwater on the tomatoes...might as well give it the fish first. Ciao