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Algae Filtration: Method of Nutrient Removal in Reef Aquaria

By Patrick Ferguson

Very regularly in the various forums on the internet questions arise about how to keep the home reef aquaria water quality pristine. Nowadays there is an assortment of ways to remove nutrients from our reef aquariums, including foam fractionation or skimming and mechanical forms of filtration.

In this article we are not going to talk about all those other methods since they've been used so extensively and spoke about so often. Instead, we will be covering a fairly new topic, one that has been touched upon by such notables as Ron Shimek and Rob Toonen.

The topic of this article is using algae as filtration in your system to remove nutrients. There are various ways of going about this; from setting up a little section in your sump with a fluorescent light over it to more complex ways like algal turf scrubbers, with each finding its own varying success.

I chose this alga because it is so commonly brought into local fish shops and found on the reef itself. So this alga isn’t “foreign” to the reef ecosystem. I was also in need of finding a cheap alternative to remove nutrients from my reef systems.

The alga noted in The Marine Coral Reef Aquarium by Fossa & Nilsen.
"Caulerpa racemosa is among the more popular species in marine aquaristics. It is often found in coral reefs in tropical and subtropical areas all over the world. Usually it has a thallus that consists of many "spheres", yet it grows in very variable forms and there are so many that it is difficult to obtain a general idea of them. In the aquarium, C. racemosa is usually easy to keep".

I began using this method of nutrient removal in my 25g microcosm roughly 9 months ago to improve water parameters. My skimmer which was a venturi run CPR Bac Pak 2 hang on the back seemed to be lacking. I received some Caulerpa from the local fish shop for free and tossed it in. It began growing at an excellent pace and didn't stop. As it grew I found that the corals located in its general vicinity were highly irritated by its aggressive growth and contact. I found its continued growth into my Xenia and other corals problematic. I began pruning it back but that really didn't seem to solve the problem. If I pruned it back too much it wouldn't show up again for a few weeks. If I didn't prune enough it would show up in a few days and cause the same destruction. Then the day came that enough was enough and I removed the entire lot of Caulerpa and returned it to my local fish shop.

I later had a creative thought of placing the alga in the return compartment of the Bak Pak. You would be able to place a small powercompact bulb over it. This would also rid the annoying bubbles from returning into the tank.

Undaunted I then setup my 50g system with a 27g sump underneath and partitioned the sump into three sections so that the Caulerpa fit into one section, the skimmer into another and the return pump in the third.

This turned out to be a good idea even if I didn't setup my Caulerpa section I still had "baffles" in place to remove air bubbles from returning back to the main system.

After 5 months of the system running adequately with another venturi “The Big Mombassa”. I found that the small bioload maintained within my system was the maximum for this skimmer. I decided I had to order a new skimmer and that I did. I purchased the DAS BX-2 and found that it performed extremely well on the system.

After approximately one month with the new skimmer running a good friend of mine came up for a visit and brought along some C. racemosa . This would improve the removal of nutrients and hopefully add lots of fauna to the system while having a small "refuge" or refugium of sorts for the various detrivores.

I found that the fauna can then breed and there populations are only dictated by the food input of the system. The refugium was lit by four 24" Normal Output Fluorescents which were comprised of four 5000k General Electric daylight bulbs. The C. racemosa seemed to acclimate and survive, but it was being out performed by the large skimmer that was located beside it.

I decided to improve the colonies removal of nutrients by replacing the old lighting with a 175w metal halide pendant. This was placed over the sump and cycled via reverse daylight photosynthesis. I have found this to keep the ph in my system more constant according to a constant photoperiod. After this upgrade I found the C. racemosa thrive.

One of the downfalls of using Caulerpa in a closed system is that the colony can “go asexual”. There are many reasons for this to occur including stripping the system of all dissolved organics. One suggestion found to help override the asexual process is to run lighting twenty-four hours a day seven days a week. As well prune the alga back frequently which will completely remove the nutrients from the system and will encourage new growth. I have never had any Caulerpa go asexual thus far so I really can't comment on it. People I have spoken to about it state that, the water goes white and the oxygen levels in the system will lower endangering animals. In this situation the best solution would be to do add carbon aggressively and do a large water change.

It is now 3 months since my addition of the C. racemosa and I have found that its growth rate is astounding and the amount of skimmate the skimmer is producing seems to be less. More and more growth is coming from the algae. This puts my $600.00 skimmer to shame in alot of ways but it also helps one to realize that we don't need alot of skimming to run a reef system. Using an effective alga will do an excellent job.

Additional Resources

C.O.M - Nice article on this alga. In French.

Gattuso J.-P. & Jaubert J., 1985. Photosynthesis and respiration of Caulerpa racemosa (Chlorophyceae, Caulerpales) grown in aquaria effects of light and temperature. Botanica Marina 28 327-332.

Created by liquid
Last modified 2006-11-24 18:41