Using a plenum in a reef aquarium

Plenums

I would appreciate your opinion on using the plenum method in a reef system.

You have to ask yourself why a plenum/live sand filter is useful? Most claim it to be a complete nitrification and denitrification system and for the most part it is. However, so is an all liverock or Berlin system. The fact is, virtually complete biological filtration (nitrification and denitrification to nitrogen gas)will take place in both methods. IMO problems occur when one adds more than 2 LB per gallon of sand or rock.My best expression of this is the system becomes biologically dense i.e.: too much area for bacteria to colonize and detritus to accumulate without enough water volume ratio and turnover.

My suggestion is to have 1.5 to 1.75 LB of sand or rock. This seems to be a good rule of thumb ratio - material to water. As an example a 55 gallon plenum system takes 80 lb. of sand for the required minimum thickness of 2 1/2 inches and comes out to 1.45 lb. per gallon.So, using the rule of thumb of LB per gal doesn't leave much for live rock. It then becomes a different looking tank. Even if you decide to overshoot the suggested LB per gal and place rock on the sand and corals on the rock then IMO you begin to have dead spots under and behind the rock where detritus cant not be removed W/O moving animals around. This is just my opinion and what I personally experienced. I have an aversion to detritus and believe in constant removing of waste important.This is best achieved using my eggcrate method which basically is a framework of eggcrate material cleverly designed and incorporating a spray bar as the main return to the bottom rear of the tank pushing all detritus to the front for easy removal.

On the other hand...some people are absolutely unconcerned about detritus.

I would like your opinion on using a NNR system with it. Was this system preferred before the new high efficiency skimmers were available?

I believe it was found to harbor denitrifying bacteria and very low nitrates and then deemed a breakthrough for denitrification. Years ago, It was thought to stuff as much live rock as could fit in the tank to achieve nitrification and denitrification (a little is good more must be better) the result was having hobbyists tanks that were setup for 1 yr. to 18 months to have unexplainable unmanageable algae outbreaks. This was then attributed to having too much rock where nutrients build up unseen.It also turned otherwise good quality rock to base rock as lighting wasn't able to get to the stacked rock. This meant a complete takedown and 75% water change and removal of un necessary rock. At that point a rule of thumb was established.

I was told that the ETS could starve some soft corals. Was this bad info?

That all depends who you talk with and what group you want to subscribe to and what type of maintenance schedule is involved.One of the most significant agreed upon points is, that there are as many methods of keeping a reef as there are people doing it. Personally I have a large ETS and almost all soft corals with no ill effects at all. A monthly WC of say 15% with a high quality salt along with regular kalk, strontium and iodine additions and high turnover rates of water in the tank and proper lighting does the trick for me.

Potential problems with plenums

Yes, I too have had an persistent algae problem while running a NNR plenum system. This occurred at approx one year to 14 months. I “unscientifically” attributed the problem to detritus buildup and high nutrient levels. I then took the system down, re-setup with a bare bottom, raised rock system and the algae disappeared. I find this discussion very interesting regarding the “success” of this type of system. Can all this be a coincidence? I don't think so. This NNR as I understood it was to eliminate/drastically reduce waterchanges. A “too good to be true” system. NNR or natural nitrate reduction is, I would think, just what it says. We all know that nitrate will get reduced with the correct amount of “live” rock or sand in relation to the bio-load of the tank. It is my opinion using the *correct* amount will have a large role in the long term “success” of the aquarium. I use and recommend 1.5 to 1.75 lb. per gal. Using too much live sand or rock can trap debris/detritus going unseen and building up a food source for micro-algae as well as being unfavorably biologically dense for the enclosed system. In my system ( a55 gall) , the 1.75 “ approx sand thickness came out to be 80lbs or 1.45 lbs per gallon. I also added approx 50 lb of live rock bringing it to over 2.36 lbs per gallon. This leads me to believe that excessive biological medium ie:live sand or rock becomes “un-manageable” regarding nutrient build-up over extended periods of time. This is Jauberts patent site

I was planning on having my rock over a 2-3" layer of sand. This would give the advantages of sand but not have the sand compressed. I really want to have the added biome of sand.

You can have some sand in the front but by using the liverock...sand is un necessary you can use *some* but 2-3 in....?? I wouldn't bother. Unless as in the book you *primarily* use sand to make up the Lbs per gal and less rock Ok but not both Just my opinion Look at my survey, see the substrate *most* people use and FWIW only a few there are readers of mine

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