Bob replies...

Hi Gordon

Thanks for your letter, and the addition of activated carbon itself has nothing to do with your nitrates increasing. However, keep in mind that its bed(s), that is to say its particles, will contain/colonize nitrifying bacteria with that resulting in some nitrate entering the system. Yet I doubt the existence of a bed of activated carbon would have the results mentioned in your letter. Just keep in mind to use small beds and rotate them as mentioned in my booklet. From what I can gather from your letter is that there's a possibility the increase may be from a previous inefficient protein skimming method (processing too small a quantity of aquarium water). Or possibly the use of too much live rock through much of the tank's existence and/or the deep bed is finally becoming saturated with nutrients. And it appears from your letter that filtration has solely depended upon the sandbed and the live rock, as you did not employ any other filtration devices or media, or even mention vacuuming the bed periodically.

Too much rock itself, and/or the covering of too much sandbed surface simply creates a lot of truly anaerobic areas where it majority of the less efficient microbes reduce nitrate only to ammonium. And if so, this ammonium in the sandbed can be recycled back to nitrate and diffuse upward in the sandbed, entering the bulk water.

And if the previous skimmer hookup was not adequately keeping pace with skimming the larger percentage of bulk water, it could have allowed too many nutrients to go unprocessed and result in some of the nitrate buildup.

Then there's the deep bed directly on the aquarium bottom. I don't want to get into the microbial processes occurring in a bed directly on the bottom of the aquarium as it is all explained in some of my booklets, especially the Natural Aquarium Booklet. Could well be the deep bed is finally becoming nutrient saturated, especially if its not adequately vacuumed periodically. And as explained above, nitrate may be leaching upwards. I would suggest better care of the bed be taken by vacuuming it once per month.

I'm going to assume when testing you know the difference between the nitrate molecule and nitrate nitrogen as you have read my booklets. And I have also personally seen Xenia become sensitive to higher nitrate levels. It appears to be a good indicator, such as in your tank that something has to be done to lower it.

As for reducing nitrate, I have tried a couple of different methods with very good success. About ten years ago I had a 75 gallon that contained a large lionfish, moray eel, and triggerfish. Its nitrate was always near 100 ppm, yet none of the fishes appeared interested in anything but three meals a day. Even though most fish are not overly bothered with high nitrate levels, you have some invertebrate that is no doubt being bothered by the growing nitrate level. In that old aquarium, I began using a plastic chip-like media called Nitrex, which is made by Aquarium Products. I placed half a box of it in another product of theirs called the 'Nitrex Box.' One box of media will handle a 60 gallon aquarium, where it oxidizes nitrate back to elemental nitrogen gas. In fact, within a few days you could see the nitrogen bubbles escaping the opening in the so-called Nitrex Box. I used three boxes as an experiment in my 75 and was able to reduce nitrate to about 40 ppm. One Nitrex Box was followed in thirty days by another Nitrex Box. Then thirty days later another Nitrex Box was placed in the aquarium. Thereafter each Box had its half box of media changed every thirty days. Its still sold and can be found in mail order catalogs. I would consider this a fairly cost effective way to reduce your nitrate level.

If you want to go high tech, suggest trying one of the newer sulfur denitrating systems. The process used in these reactors is not like those used in most other denitrifying devices. The majority of these other devices use 'anaerobic' heterotrophs, which must be fed a carbon source such as methanol or ethanol. Actually, Vodka has been one of my past preferred carbon food sources in a home built unit I made several years ago. Their feeding process needed to be carefully controlled to prevent hydrogen sulfide or nitrite being returned to the aquarium. Too much of the carbon source material resulted in hydrogen sulfide, too little resulted in nitrite and/or the nitrate simply returning to the aquarium. And the flow of the water stream through this and similar devices was also very critical, usually requiring constant tweaking to make sure the right amount of 'food' was being provided to the bacteria that colonized the substrate medium in the reaction chamber that the water flowed through. Really a constant pain in the you know where to control and quite dangerous if not correctly controlled.

Sulfur reactors are fairly new and use a process called 'autotrophic' bacteria sulfur denitrification. Small beads of sulfur are placed in a contact chamber and aquarium water flows slowly upward through the device. As the water rises in the contact chamber, bacteria on its sulfur substrate media begin to remove dissolved oxygen in the water, thereby making the area more anaerobic. When this occurs, the bacteria further up in the contact chamber go after the oxygen that is part of the nitrate compound. When the water exits the top of the device, nitrate is greatly reduced. How much reduced depends upon the level of the nitrate entering the device. The nitrogen gas resulting from this process exits from the device at its top area.

Keep in mind the reaction releases excessive hydrogen ions, which makes the exiting water very acidic. It is also believed that the process produces carbon dioxide, and all can easily lower the pH of the exiting fluid and also its calcium and/or alkalinity levels.

Another problem area with this process is the production of sulfate in the exiting water. It must be removed so as not to skew the ionic balance of the seawater in the aquarium. Therefore the effluent from the sulfur reactor should be flowed through a chamber filled with crushed coral, preferably one of the better grade calcium reactor media. This will help precipitate most of the sulfate, and since the water is acidic, release some of the calcium carbonates in the media thereby raising its pH. Much like a calcium reactor does, except without the use of a separate CO2 input. However, as I have not personally tried it, the media it passes through is said to fairly quickly turn to muck. Therefore it must be changed out as needed.

As with previous type denitrating devices, the speed of the water flow through the device is critical. Too high a flow results in nitrate being returned to the aquarium, too little flow results in hydrogen sulfide or nitrite being returned to the aquarium. Therefore its important to test the effluent every few days when first starting these type units until the right flow rate is found. Otherwise, after that, these unit require little attention except periodical effluent testing. And once the aquariums nitrate level is within the preferred level, a slightly faster water flow should be considered. However, that does depend on how much food is entering the aquarium. The instructions coming with the device should closely be followed.

And even though sulfur is one of the greater quantity elements in the bulk water, periodic water changes should be part of your standard maintenance chores. Also, since the effluent from these type reactors is very acidic, there needs to be additional attention to calcium and alkalinity levels and supplemented as needed. A calcium reactor would be an extremely good addition if a sulfur reactor were utilized.

Since I have not used this type equipment, and only know of one company offering it, suggest visiting d-daquariumsolutions.com and checking it out. I'm sure they could supply some additional information if interested.

As for over skimming, that is possible but probably rarely ever happens. If you see the skimmer taking out little waste when running full time, use it only from 6 PM to 8 AM. Of course a good trace element solution is another cure for that problem area, but don't over use as that can lead to unwanted algae.

Hope this helps and keep me posted.

Bob