Saltcorner
By Bob Goemans
By Bob Goemans
Hi Bob,
I was reading your reply to one of the reader's questions regarding the set up of 180 gallon show tank with a 75 gallon plenum and came across something that I didn't understand. You said the overflow from the main tank to plenum tank should be half of that 75 gallon volume, which is about 40 GPH. My main set up is a 44 gallon tall reef tank with a 20 gallon plenum/refugium tank with build-in wet/dry filter. This offers double bio filtration, which is good - wouldn't you agree?
I use a Rio 1700 powerhead to flow water from the plenum to upper tank. From the manufacture chart my pump or overflow rate would be about 250GPH (the only source of water flow in main tank at this time). The wet/dry filter has a separate pump.
As for the plenum setup: 1.5" deep plastic grid, 1" of 2mm crush shell, 1" of 1.5 mm gravel, 1.5" of 1 mm gravel, 1" of fine sand, and about 0.3" of ultra fine sand, plus a couple pieces of life rock and some macro algae. As for main tank, I have 3' of fine sand and about 20 pounds of live rock. The system doesn't have a protein skimmer at this time and the major source of light is indirect bright natural sunlight. The tank has been running for about a month without a major algae outbreak. One candy coral I placed in the tank two weeks ago is looking real good and the mushroom corals are looking great also (one is 2+ inches in diameter!) Last time I checked, no detectable nitrite, little bit of nitrate and ammonia.
In your opinion, should I lower the overflow rate to 10 GPH and why do you recommend a slow return water flow? That means I would have to run a different power pump to increase water flow in the main tank (more $ for electric bill+heat!) I also just started to run UV light this week to control Ich problems. Will that affect the system's bio-filtration ability? Any other suggestions that you could provide to make the system better, reduce maintenance and lower its operation costs would be appreciated. Thank you!
Tony
Los Angeles, CA
Hi Tony,
Thanks for your letter and can understand the confusion! There are many different ways to set up aquariums where main system water flows to smaller sump-like systems. The problem here is that the purpose of the smaller interconnected tank needs to be resolved before its brought into play. Will it be a tank to house equipment, e.g., protein skimmer, trickle filter, etc., or a refugium of some type, or will it simply be an interconnected plenum style biological filter. It can't or shouldn't be all three! Where my past 180 gallon system was concerned, I felt that its 60 gallon interconnected plenum system was all the additional biological filtration my system needed. Most of the system's nitrification occurred in the main system's shallow course grained (2 - 4mm) sandbed and the resultant nitrate was either somewhat acted upon in its deeper areas or much more efficiently in the below plenum system. Water movement in the main system was provided by Tunze powerheads, which more than adequately took care of circulation in the main system.
As for flow rate between an interconnected plenum system and a main show tank, it would make no sense to speed the water through the interconnected plenum system. Past history has shown that if water was pumped between systems at very high rates, i.e., above the volume of the plenum system, there was usually less reduction of the incoming nitrate. Not a scientific finding, however, something that has shown itself to be evident over the past five or six years where auxiliary plenum systems have been used. Keep in mind the same premise is true where protein skimmers are involved! Where interconnected plenums are concern, it appears that adequate "dwell time" has an apparent valve.
Also, in my opinion, the use of a trickle filter, placed anywhere in a plenum system, is counterproductive. Why allow its nitrate to be discharged into the bulk water. Enough will be produced by the sandbeds, where hopefully most of it will diffuse downward and be reduced.
As for the sand used, it appears better suited for a macroalgae style refugium, as the very fine sand will halt diffusion and cause the bed to become anaerobic where only ammonium, an algae nutrient will be produced. And I should add there is no need to use different size sand grains in the plenum bed. Where that misinformation came from remains a mystery, but is totally incorrect. All of the sand should be in the range of 2 - 5mm. Also, if the sand is very fine in the main system, the same may happen there. If you want to grow macroalgae, then you want a fairly nutrient rich environment. If you want a fairly nutrient poor environment, then a properly constructed plenum system will help attain that goal. But your plenum bed is 'not' what a 'plenum' bed should be! Make a choice as to what function the smaller tank will serve.
The UV will not harm already established bacteria colonies, however, it doesn't sound like yours are fully established yet. Could be its use will slow further nitrification bacteria colonization. And, it will kill useful bacteria and algae cells in the water that passes through it that coral could feed upon. It is not the answer when it comes to curing a Marine Ich problem. If the situation is not too severe, consider getting a couple of cleaner shrimp such as Lysmata amboinensis. They will help pick off the parasites before they can multiply, and have successfully prevented major outbreaks in many aquaria. New systems usually look good for the first six months, however, its what happens to them after that, that will tell how good your planning and husbandry methods are! Visit my website and go to the "Guest Articles" page and read the Sandbed Articles Part I & II. You may find the information posted there quite helpful.
Hope this helps,
Bob
