My Diminutive Algae Scrubber

I had my glass aquarium built for me with a few additions inside. At the left end is a small triangular area which contains four pumps and also the intakes for canister filters, an anti-phosphate filter, a denitrator (not now in use), and a protein skimmer.

The skimmer is a hang-on type which fitted except that the outlet, which flows down a flat surface, was not long enough. Anyway, the supplied flat plate outlet wouldn’t go down into the aquarium as the side-strap got in the way.

“Hmm” I thought, engaging super Do It Yourself brain cell.

After doing a few measurements I went to the LFS and had some bits of glass cut to act as barriers to seawater. When these were supplied I siliconed them into place on the side brace on each side of the skimmer outlet and also behind it.

Then I obtained some rigid plastic and cut a piece of the correct length to reach the seawater after bending over the side strap. Easily done, however I was left with a length of straight plastic when I needed a bent one.

A piece of cardboard was obtained and bent to the angle required. Then I got my blow torch out (normally used for plumbing) and carefully heated the plastic at the bend point, with the plastic over the edge of a piece of thin metal. This was the part where I thought the plastic would be ruined. But no, keeping the flame of the burner away from the plastic I managed to bend it correctly. Now it was cup of coffee time – very pleased.

The old plate outlet was cut off leaving only a fairly short flat piece close to the skimmer, and the new plate was then glued to the remaining part. When the glue was fully set, the skimmer was switched on and everything worked, with the returning seawater going into the aquarium silently.

I realized that this run of seawater over the flat plate would be a good air/water interchange and so be useful in ensuring a good oxygen level. The original need though was just to get the seawater back into the aquarium properly and quietly.

The return plate sits close to the bank of fluorescent tubes, and what I hadn’t considered was algae. This began to develop on the plate and I managed to keep the plate clean for quite a while as part of normal maintenance.

I noticed that the algae developing was not the green and hairy stuff but much darker, wiry and short. So I stopped cleaning it to see what developed.

The algae developed all over the slope of the plate and as said was the short dark wiry type often called turf algae. I kept a very close eye on it but it didn’t get out of control. In fact, once it had got to 1/4″ or thereabouts it didn’t get any longer. There wasn’t any die-back either. The alga hasn’t entered the aquarium area at all.

The photo I’ve taken is rather ‘blue’ probably because it was taken directly beneath the fluorescent tubes which include actinic types.


The aquarium has been running for a bit over six years and the skimmer the same. There has never been a problem generated by the algae on the skimmer return plate.

I do seawater tests for nitrate and phosphate, and these are usually done monthly. The tests indicate zero, though of course with hobby test kits it is better to say ‘undetected’ as the kits are not of a scientific standard. The algae on the skimmer outlet plate must be finding nutrients of some sort to survive, so perhaps there is a very low presence of nitrate and/or phosphate. The seawater flow is clearly to its liking and there must be a high oxygen presence.

Algae scrubbers are a well known method of nutrient control. The modern type is the sump which is planted with Caulerpa macro algae. They are bigger than my little algae covered plate!

I never intended to have an ‘algae scrubber’, but have now got one of sorts. It is very small but nevertheless will be doing something towards maintaining seawater quality.