Saltcorner
By Bob Goemans
By Bob Goemans
Dear Dr. Goemans,
My name is Patrick Jenkins, and everyone calls me Pat. I hope you don't mind me writing to you about my newly set-up 55 gallon aquarium. I thank you for all of the articles you have written on this subject, unfortunately most of my literature is in storage at this time and quite frankly I'm not sure which boxes they are in. I am sure you are quite busy and if you cannot answer this E-mail at this time I will understand. I have set the tank up as a plenum system.
This 55 gallon acrylic aquarium system came with a built in overflow, variable output pumps, a bio tower and media, and a protein skimmer (airstone type) being fed from sump with a powerhead. There is DLS in the overflow tower and two 350 GPH powerheads for water movement.
There's about 100 pounds of mixed substrate: 40 pounds of crushed coral and shells, 40 pounds of a smaller type supposedly already bio activated, 20 pounds of what's supposed to be aragonite sand (no brand name), and 10 pounds of substrate from a 10 gallon tank I tore down when I set this one up. My guess of the average grain size is 2 to 4 mm
A homemade plenum sets on the bottom of the aquarium consisting of three lengths of 1" PVC conduit drilled on all four sides every 2" to 3" and covered by 1/2" eggcrate wrapped by plastic window screen. The substrate depth above the plenum averages about 4 1/2" to 61/2". There is also a layer of screen about 2" below the surface of the substrate to prevent disturbance of the lower level by animals.
Approximately 45 pounds of live rock is setting on 3" diameter x 1 1/2" high PVC rings (6 of them) that are sunk to the dividing screen described above. There is also 35 pounds of rock, which is newly bought and mostly cured from a local fish store. The rest is 4 years old from the10 gallon tank I tore down.
At this time the lighting is only 60 watts, but I have purchased a 250W 6500K metal halide and a do-it-yourself kit and am building a canopy. Eventual wattage will be at least 310W.
The tank was filled with synthetic seawater made with tap water, My local tap water is fairly low in dissolved organics, its ammonia is undetectable, nitrate is 2.2 ppm, pH 8.2, and alkalinity only reads 1.2. I do have an R/O drinking water system and will use it for make up and water changes. It doesn't have a DI cartridge so it doesn't help with the nitrate in the tap water.
There are two fishes , a 3" purple tang and a 2 1/2" Kole tang. There are also two brittle stars about 5" from tip to tip and two turbo snails. All animals were transferred from the 10 gallon. Except for maybe a conch or two I'm not going to add any animals for at least the next two months. There are no photosynthetic animals.
I have some questions:
1. I thought I read an article by you where you advised removing the bio-media from the sump , but I cannot seem to locate it. Is this right? Should I remove it? What should I use in its place?
2. On the right rear side of the tank I didn't get sand between the end of the plenum and the glass side of the tank. There is about a 1" square area where I can see into the plenum. Should I be concerned about this?
3. Are there any problems with this set-up that you can see from my description?
4. Is this enough info?
I thank you for any advice you may offer.
Sincerely,
Patrick Jenkins
Hi Pat,
Thanks for your letter and everybody calls me 'Bob.' Let's first begin with your questions, and then I'll add a few comments that may help you have long-term success.
Your exactly right about removing the media, whether bio-balls or DLS from the bio towers. It does not make sense to generate nitrate, which is the end result from this type media, and allow it to enter the bulk water of the system. It is far better for the entire system, including the animals, if the nitrate is produced in the oxic layer of the sand (its first half inch) and then allowed to diffuse downward into the anoxic portion of the sandbed where it is totally oxidized. Why dump it into the bulk water - that's simply not a logical approach, especially in reef systems! As for replacing it with something, I would recommend using activated carbon and a quality phosphate removing compound somewhere in the system, probably in the sump where water can slowly flow through them. If prefiltering of the water before it reaches the sump is desired, I would recommend using a section of 'blue-bonded' filtering material and washing it clean at least weekly.
If the plenum system was started with all dead sand, bio media in the towers would help with additional sites for nitrification bacteria, and cycling time may be reduced somewhat. However, a couple of months later when the plenum's sandbed becomes established, the removal of the plastic bio media should begin. If live sand and rock is used to start the plenum system, the plastic bio media becomes an unnecessary addition and not in the best interest of the environment.
As for the small amount of light that enters into the plenum, that's not a problem. Only if most of the plenum area were open to light would I be concerned. In those cases, I recommend some black tape (like electrical tape) or wood trim being applied along the open outside glass area to prevent light entering. As for sandbed depth, 6.5 inches is far too much because oxygen penetration, which is the key to plenum sandbed efficiency, may be insufficient in the deeper zones. Try to stay in the four-inch range, give or take an inch.
I'm not sure if the rock PVC 'lifts' are necessary. That would depend on the shape of the rock. If they were basically flat-shaped, then the lifts may be ok, however, they also should be drilled with many holes to allow for circulation between its inner area and the surrounding bulk water. I really prefer the use of branching rock in most reef aquariums as it allows for better water circulation.
Depending where your goal for this system goes, you may want to consider a calcium reactor so as to reduce dependence on calcium and buffer additives. A reactor will create a very positive effect for stony corals and some soft corals. Also, a quality RO/DI, dedicated to aquarium use, would be on my list of equipment additions, as the tap water supply in this country, in my opinion, continues to go downhill. And airstone skimmers, again in my opinion, went out of style with the dinosaurs! There's no doubt in my mind your system should have something much better than what you now have. If you want some brand recommendations for these 'tools' let me know.
Hope this helps, and keep me posted,
Bob
