clayswim said:
I think what I was getting at originally was that wet/dry filters impede denitrification when compared to live rock only. After all these long messages in both threads I'm not even sure if MikeS agrees with that or not
I guess the discussion was how it happens in the first place.
Ok, back to the orgional question and or difference of opinion on it...why does the wet/dry filter tend to produce higher levels of nitrate when added to an existing tank full of live rock? Your contention (please correct me if I misinturpeted what you were saying) was that the bacteria present on the bioballs outcompete the bacteria present on the live rock to the extreme where basically the bacterial activity in and on the rock is halted, and no more nitrate reduction is taking place, thus increasing the levels seen in the tank, correct?
My contention was that the addition of the wet/dry creates a situation where it is rapidly processing available nutrients into nitrate before they have a chance to be removed by other means, like skimming or water changes.
basically, I disagreed with three main points of yours as reasoning behind how this occurs. After a discussion with mojo this morning, (btw thanks for the contact Mike, it was a much welcomed addition to an otherwise crappy day at work
)I still disagree with two of your points Clay, and the third I think we both were perhaps correct, but still missed the mark...
On your first two points, you contended that the bioballs outcompete the LR to the point where there was basically no significant bacterial activity taking place, and one of the main reasons they were able to do this was that water flow across the LR limited the amount of surface area available to the bacteria to grow. I still disagree with both of these assumptions. Flow is not going to negatively impact bacterial populations. These bacteria are not simply sitting on the rock waiting to float away or get blown off the rock, they are in a biofilm that coats the rock. This biofilm is not easily removed, either. So flow isn't going to limit available surface area for bacteria on the rock. The bacteria are staying on the rock, and these bacteria even with a wet/dry working away are still being exposed to nutrients and oxygenated water. Granted, the wet/dry is definately a better environment for bacterial growth, I think we have all been in agreement on this point from the beginning, but this is primarily due to the constant flow of highly oxygenated water through it, not the fact that the LR is a less suitable surface to grow on because of flow. Plenty of bacteria will remain on the rock, the competition from the bioballs simply isn't going to reduce them to the point where activity halts altogether.
Ok...the third point was the one about LR alone not producing nitrates. This one I think we were both off a bit. I asked Mike about it this morning, (please correct anything I don't paraphrase correctly Mike
) He feels it is possible for LR alone to reach a balance between nitrate production and reduction, but that there are a good number of factors that can skew this balance one direction or another, like nutrients, water flow and oxygen levels, interference from ammonia, ect. Sometimes you hit the balance, sometimes you don't. I'll meet you half way on this one Clay...
Ok...so I think it's safe for me to procede under my origional assumption that LR will still have viable bacterial populations and will still reduce nitrate...I will now however concede that the wet/dry can have a negative impact on LR bacterial populations to a degree. On this impact and its effect on the rocks ability to reduce nitrate, I think the proximity idea does in fact make a lot of sense, I'm willing to go along with that one...
Ok..., I guess for me the question now becomes to what degree does the bacterial skew towards the wet/dry impact the nitrate reducing capacity of the LR, and in turn to what degree is this reducion responsible for the rise in nitrates that is typically observed when a wet/dry is added to a system? I still think that the rapid rate of nutrient process in the wet/dry has a lot to do with the raise in nitrates, but I can see that the reduction in denitrification will contribute as well...
I suspect the answer will have a great deal to do with the individual system in question to start with...ie a tank with lots of LR and a reletively small wet/dry will have a less pronounced bacterial skew, where a tank with less rock and a larger wet/dry will have a greater skew. I think the overall ratios of LR surface vs. bioball surface will have a lot of impact on the size of the skew...
MikeS