By Bob Goemans
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Bob Goemans corresponds with Barry Penner (Pleasanton, CA)

Barry Penner (Pleasanton, CA) writes...

Dear Bob,

I am a dentist and have a 50-gallon reef tank, which can be viewed from the reception area. It is in the wall and is surrounded by a picture frame that really sets off the looks of the entire tank. The rear of the tank opens into the darkroom, which is adjacent to the reception room. I use a 20-gallon tank for the sump.

Had great success as well as failure over the years with my tank. I would say that my main problem has been the growth of algae over time as the reef system matures. I have read lots of information from concerning plenum systems and of course have read your column Sand Mail in FAMA for years. For years I have wondered if a plenum system might be of help. I always hesitated though because I didn't like the idea of using up 5 - 6 inches of aquarium space for the sand system. I thought of using the sump, but didn't see how that would work either, so I ordered some of your books and read them thinking maybe I could figure out something.

Have now figured out a way to provide some additional space in the darkroom for another 20-gallon tank. I want to set it up as a plenum system with 4 inches of CaribSea Arag-Alive Florida Crushed Coral 2.0 - 5.0 mm particle sizes. My questions are:

* 1. What flow rate would you recommend for this 20-gallon tank?

* 2 Would you use a circulation pump or powerhead in this tank? If so do you have a recommendation for what to use?

* 3. Would you provide any lighting for this tank? If so, why and how much?

* 4. Would you put any organisms in this tank besides the bacteria in the gravel such as crabs, snails, etc? If so what are your recommendations?

Once this gets up and functional the plan is to replace my 50-gallon acrylic tank with a 50-gallon glass tank. At that time I want to put 1 inch of the CaribSea Arag-Alive Florida Crushed Coral 2.0 - 5.0 mm particle size on the bottom, unless you would suggest something better.

If you would like more info I would be happy to respond. Thank you for your help.

Barry Penner Pleasanton, CA

Bob replies...

Hi Barry,

Thanks for your letter and very good questions. The idea of a separate interconnected plenum solely for filtration needs is one that has 'helped' many aquarists win the war on unwanted algae. Nevertheless, more than just a plenum is needed if one wants to win this battle. It is necessary to control the systems bioload with properly controlling its fish load and the food entering the system. And in addition, controlling certain water parameters, such as the nitrogen-laden compounds, e.g., ammonium, nitrite, and nitrate, along with the all-important phosphate level, which should be < 0.015 ppm.

There's no doubt as systems age, they tend to become nutrient rich. And that's where controlling water quality is 'extremely' important. Tests for nitrite should be zero, and those for nitrate over 15 ppm are an indicator more attention needs to be paid to its bioload and water quality.

As for phosphate control, a connected canister filter dedicated to this parameter is the way to go, as excessive phosphate above that already mentioned is the greatest threat. Therefore, recommend first testing for this parameter, preferably using a Salifert test kit or that sold by Merck. If greater than mentioned above, purchase a small canister filter and use one of the newer iron based products, such as ROWAphos, to get it under control. If you need information on how to use these products in a canister filter, contact me and I'll explain how I use it in my canister filter.

If nitrate is above that mentioned, then question the number and size of fish in the aquarium, and the amount and types of food fed. You don't mention these details, but if excessive, then that's a good place to begin getting the algae problem under control, as once the input of excessive nutrients is stopped, and existing too high nutrient water parameters are back under control, the war is almost won. I say almost, as the existing growths will have to be removed by hand, as some of these are capable of generating their own nutrients once they become larger.

Then, the interconnected un-lit plenum is the perfect choice to keep nutrients such as nitrate almost non-detectable, as is the case in my present aquarium. As for the choice of a pump to supply flow between your 20-gallon plenum and main tank, that would depend on the 'lift' or head pressure it needs to develop to lift the water high enough to reach the main tank at the desired flow rate, which should be between 10 - 20GPH. And the plenum system, without the dividing screen as that is not needed in this setup, does not need any organisms such as snails, hermits, or crabs to remain functional. Keep in mind I do not sell products, but maybe if did, would suggest them and others. But honestly, nothing additional is needed where this plenum is concerned in my opinion.

Your sand choices are perfect in all situations. Also, I've had letters noting the success of a product called 'Algae Magic,' which over time seems to dissipate unwanted growths. So you might want to try it and let me know after using it for a month or two your results.

As in your profession, good dental hygiene is the bottom line when it comes to having a healthy set of choppers! The aquariums bioload and water quality factors are similar hygienics when it comes to keeping an alga free aquarium!

Hope this helps,


Barry Penner (Pleasanton, CA) writes...

Dear Bob,

Here is a follow up: I installed a 20-gallon tank as an auxiliary filter. It has a 1.5 inch plenum and 4 inches of CaribSea Arag-Alive Florida Crushed Coral. The flow rate is between 15 and 20 gallons per hour. No lighting and nothing besides saltwater and coral in filter. My nitrates went from 15 down to Zero in less than two weeks. I am scrubbing spots on the rocks that have a heavy growth of algae and it appears that I am slowly winning the battle. I will update you in the future.



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