<a href=showthread.php?s=&postid=11692733#post11692733 target=_blank>Originally posted</a> by CJBDFRAZ
I have notice that the DIY denitrifier uses bioballs. and I have seen in my experience with using a wet/dry filter that after almost a year of use, the bioballs will raise your nitrates. I would keep an eye on that.
This isn't quite the same issue though, I think. It isn't the bioballs per se that cause high nitrates, it's the application they are being used in.
Anyway, correct me if I'm wrong here, but heres how I understand it....
In their usual application (i.e. a wet/dry) bioballs they are extremely effective at converting nitrite to nitrate: they provide the large amount of surface area necessary to host lots of aerobic ammonia/nitrite eating bacteria. This is, especially in a Fish-Only type tank where nitrates are far less of a big deal, a great thing: they can keep up with even very high outputs of fish poop like gangbusters and keep fish from poisoning themselves. The caveat is, of course, that because wet/dries are super oxygenated environments, they do almost nothing as far as turning nitrate into harmless nitrogen. They really are nitrate factories in that their job is, literally, to produce nitrates (by getting rid of the much more toxic precursors).
This is, however, also why they are no longer recommended for reef tanks. When you don't have to worry about handling huge amounts of fish poop (i.e. tons of deadly ammonia), fuges/live rock/deep sand beds are superior in the sense that, while more delicate, they can help handle the entire range of the nitrogen cycle, meaning that a 0 nitrate tank is far easier to maintain.
In this sort of system, a wet dry with bioballs is going to produce nitrates primarily just because all the work has already been done by the live rock, etc.: meaning that the bioballs are basically now not doing much OTHER than catching and holding decaying materials (and keeping them away from the protein skimmer until its too late).
Now, in a coil denitrifier however, it's almost the exact opposite. By the time the water hits the bioball section in this setup, there is almost no conversion from nitrite to nitrate going on at all (usually this stops in the last 1/4 of the tubing). It's all conversion from nitrate to nitrogen at this stage, and the bioballs are not going to be creating any nitrates in this application. As long as the system is built right, they will be destroying them: and quite effectively.
You also normally keep gunk out of a denitrifier entirely (unlike with wet dry bioballs, which are often the very first thing that dirty drain water from the tank hits).
What I've heard as far as complaints about with denitrifiers is that figuring out the perfect flow rate is very tricky at the outset. Too slow, and that super-low oxygen environment can cause completely different toxic compounds (ones that we don't even test for) to form. Too fast and nothing will happen. You really have to buy a good pump/valve system so that you can fine tune it precisely (you tune the output of the pump going into the denitrifier), and then test the output so that you are just on the cusp of getting a 0 nitrate output from a higher nitrate input.
The ph is also a concern, because the output drips will be lower in ph than the input, meaning it's dropping your ph in the tank over time (albeit very slowly). Most people I've heard of that have success with these systems also have some sort of ph buffer/calcium reactor going at the same time.
Also keep in mind that these systems have to cycle, just like a tank, and most DIY plans say that it can take up to 6 weeks until all the right bacteria are in the right places.
