My experience with lower nitrates in my reef tanks has been an ongoing battle that started just a few months into the hobby. My first tank was a 29 tall with a 20 sump. Almost everything on the tank was diy and I spent as little money as possible. I dosed with baking soda, calcium chloride (driveway melter), and Epsom salt from Walgreens. When that tank was running I used gfo to lower phosphates, but relied on water changes to lower the nitrates. It wasn’t until I set up my current tank that I started to learn about diy ways to lower your nitrates. Once I got sick of doing water changes on my newly set up 120-gallon tank, I started doing research on ways to lower nitrates. My first attempt at this other than macro algae was the coil denitrator. The idea behind this is to buy a bunch of ¼’’ poly tubing, maybe 25 to 50 feet, wrapped around a pvc pipe roughly 3’’x12’’, fill the pvc with some type of bacteria inhabitable media (I used matrix rock). These dimensions are what I used for a volume of 150 gallons, although this didn’t work for me many people have had a lot of success with this, my main issue was the volume, bigger volume makes it a lot easier. I just want to explain the idea and my experience with it so it can help you.
Lowering Nitrates with a Coil Denitrator
So the way the coil denitrator works is your input is at the beginning of the long ¼” tubing, which then flows into the main chamber, then from the main pvc chamber back into the tank. By concept the reason for the long tubing is to house aerobic bacteria, which slowly uses up the oxygen as the water flows through the long skinny tube, then sometime before the end of the tubing the oxygen is used up and anaerobic bacteria can thrive, eating that unwanted nitrate and turning into nitrogen gas, this effluent is then dripped back into the tank lowering your nitrates.
As for the starting point the rule of thumb for the volume of water through the denitrator is about 1 drop a second, after that the efficiency of the denitrator depends on the concentration as well as the nitrate production in your tank. You really have to experiment with all the variables, which include the length of ¼” tubing before the pvc, the volume of the pvc pipe, and the drip rate through the denitrator. As for me i thought I had a decent piece of equipment made but no matter what I did I couldn’t get it to become anaerobic and eat the nitrate. I’m assuming since it didn’t go anaerobic I didn’t use enough ¼’’ tubing.
Lowering Nitrates with a Sulfur Denitrator
Not long after my unsuccessful attempt at the coil denitrator I began to research sulfur denitrators. They seemed simple enough. The idea behind them is to use sulfur as a bacteria media. The bacteria use up the nitrate as long as there is a sulfur source. The sulfur is housed in an up flow recirculating reactor, this reactor then has a water in and out, and that’s it. So I got the idea to use one of my extra 10” filter housings with a bulk reef supply media cartridge (the hard type). I then plumbed a pump to make the filter housing into a recirculating reactor. Then I drilled and tapped 2 1/8” npt holes into the pvc pipe for the input and the output. I hooked the input to my main water manifold and had in going in a few hours.
Tuning a Sulfur Denitrator
Once I had the reactor going it was time for patients (which I lack sometimes). I started the flow through the reactor at 1 drop every 2 second, or there about. I tested week after week to see how it was working. Within a week it was producing very high amounts of nitrates, according to my nitrate test kit(salifert). This is good because its most likely nitrite not nitrate and the test kit is just seeing it as nitrate. The reactor has to go through the same type of bacteria bloom as our tanks do when we set them up so soon it will start eating the nitrate and turn it into nitrogen. Once a few weeks past it was producing nitrate free water. This really got me excited because by this point my nitrates in my tank were about 25-40ppm, as well as my failed attempt with the coil denitrator. This is when I began to smell the effluent. It had a rotten egg type smell. This just means that the bacteria in the reactor are eating up all the nitrates and need more! So I turned it up to 1 drop a second. This is when I began to start testing my tank to see how fast it will drop my total nitrate. To my surprise it took a very long time for it to eat up the nitrate, which I guess is good considering one doesn’t want to change anything too fast in a sps dominant reef tank, even high nutrients. It literally took months to see my nitrates go down. This was because my small reactor couldn’t handle more than 1 drop a second through it. When I tried to do 2 drops a second the reactor just didn’t have enough volume of sulfur to eat up the nitrate and it would constantly test with nitrates still in solution. This is when I decided that 1 drop a second is good enough for me and its been running on my tank ever since. The last time I checked my nitrates were under 1 so I actually turned it off, but will most likely be turning it back on once they rise again.
Lowering Nitrates Conclusion
I think that anyone battling nitrates should defiantly look into building or buying a sulfur denitrator. I believe that if you have a small reef tank a diy 10” filter housing denitrator would be great start, and if your around 150 gallons total volume, like me,you will defiantly have to build a larger volume housing, although a small type will for sure help with reducing nitrates. If I was to do this project over i would buy larger sulfur media. This is because I was being impatient and went to the local grow shop and bought a bag of sulfur prills, which are too small, in my opinion, for proper flow through the reactor, but some may think prills are better because they do allow for more surface area for bacteria. I would also build it large and out of pvc. Just recently a friend of mine put a large type calcium reactor he had laying around on a tank but the flow through the calcium reactor was so low it went anaerobic within a few days so that just goes to show that volume really does play a key role. I hope this article helps you not make the mistakes I have so you have a more enjoyable reefing experience.