Saltcorner
By Bob Goemans
By Bob Goemans
Dear Bob,
I have enjoyed & learned a lot from reading your Sand Mail in FAMA magazine. I have a serious problem with nitrate & hope you could give me some advice.
I have a 29gal marine tank set up in July 2001. It started with an Under Gravel Filter recommended by my LFS for my FO tank. The UGF is constructed similarly to your described Plenum system with eggcrate as support for the horizontal grid with 3" aragonite sand. The air-lift tube is connected to a powerhead. The only info I lack of is the size of the sand. I have slowly upgraded it by adding an addition filter & skimmer. I've also added 20 lbs of LR on top of my 20lb base rock in August 2002. During all of this time I was not aware of the nitrate (NO3) becoming an issue. It wasn't until last December 2002 when a Hair algae boom began that I came to realize I had a NO3 problem. Using a Tetra NO3 test kit, I have a reading of 100 mg/l. After much research, I realized that my UGF and/or canister filter is the culprit.
I have immediately performed 25% water change 6 times in 6 weeks. 1st water change was on 5th January 2003. And on the 7th time, 16th Feb 2003, I have performed 60% water change. But the NO3 reading still remained 100 mg/l. My LFS used 2 types of test kit & the reading was the same.
My question is, can I disconnect the Powerhead from the air-lift tube & would my UGF automatically become a Plenum System?
My current system: UGF with 3" sand run by a powerhead, 1 Ehiem 2028 Canister, 1 Red Sea Prizm Skimmer, 1 add'l powerhead for circulation, 1 UV sterilizer, 1 x 2ft ZooMed Actinic Blue Fluorescent, 1 x 2ft ZooMed 10,000k Fluorescent.
My Fish stock: 1 Long Nose Hawkfish, 1 Six-line Wrasse, 1 Blue Damsel, 1 Maroon Clown, 1 Lawnmover Blenny, and 1 Yellow Tang.
My Coral stock: 1 Brown Button, 1 Green Star Polyps, 1 Hairy Mushroom, 1 Brown Mushroom, 1 Finger Leather, 1 Leather Coral, 4 Feather Duster Tubeworms.
Last reading on 16/2/03: Temp 80F, SG 1.022, pH 8.2, dKH 9, NH4 0, NO2 0, NO3 100.
Ehiem Canister Media (top to bottom): Poly Filter, Chemi Pure Carbon, Ehiem Ehfisubstrat, Seachem De-Nitrate (added on 26/01/03), Coarse Filter pad, Fine filter pad.
Thank you for any advice you can provide me.
Best regards,
Vincent
Singapore
Hi Vincent,
If you like the column, checkout my website at www.saltcorner.com!
Thanks for your letter, and there are two different methods for reading nitrate. Some nitrate test kits measure the "nitrate ion" and others measure "nitrate nitrogen." Nitrate is a compound or combination of elements. One molecule of nitrate is composed of one nitrogen atom and three oxygen atoms. Since the atomic weight of nitrogen is 14.01 and the atomic weight of one oxygen atom is 16, the weight of one nitrate molecule equals 62.01, or 14.01 + 16 + 16 + 16. Therefore the test kit that reads the nitrate molecule (the Tetra Kit) will show a reading 4.4 times higher than a test kit that reads nitrate-nitrogen. And nitrate-nitrogen is the more correct reading. That means your real nitrate reading was slightly less than 25 ppm. Still too high though.
It would be very helpful to read my Water Quality Booklet, mentioned on my 'Bob's Books' page. And, I should note that water changes are a waste of money when it comes to reducing nitrate, as the nitrate sequestered inside live rock and in the sandbed will simply flow back into the bulk water within a day or two after the water change.
Your fish load, and therefore the food fed to support them, is more than what a microbially balanced system can handle. Reducing the fish load may help control the nitrate level in the future. As for the canister filter, I would cut the Poly-Filter into small pieces and place it and the activated carbon in the canister filter. Adding more areas for nitrification only adds to the nitrate level. As for the de-nitrate product, I would place that where there's no forced water through it, as the oxygen in the forced water will reduce its efficiency.
And, the UGF may act like a plenum and help reduce nitrate level, however, it is in no way comparable to that of a plenum grid which basically has a much more 'open' surface area. UGF plates have openings probably making up about 25% of their surface area, whereas plenum grids have about 98% of their surface open for diffusion. I think you get the message. But, in your case you can try it and see where it goes. Hope this helps,
Bob
