A couple of comments. Lowering the pH
gradually in a tank into acid levels is the exact method used to establish bacteria that do function in such water. I have put this method to use myself. One can get a tank cycles at a pH approaching 4.0 given the time and accurate pH testing. However, one of the best indicators that OTS has happened in a tank is the pH gets much lower. Ammonia does not rise old tank syndrome, other things do. The bacteria are still converting all the ammonia and nitrite. The biggest problem is when one changes the water finally all the parmeters change rapidly and by a fair amount. The balance between NH3 and NH4 which was almost all NH4 changes fast into much more NH3 as the pH rises.
And then lets dispel another misstatement, nitrate can kill fish and it will do so. It is one of the causes of OTS as well. If one fails to remove nitrate as it builds up it will create acids which cause the pH to drop. Nitrate also changes the TDS. Nitrate poisoning has the same symptoms as nitrite poisoning- fish gasp at the surface because their blood cannot carry oxygen. The difference between the nitrite and the nitrate is the size of the molecule. NO2 is smaller than NO3. And just like NH3 can pass through the gills into the fish but NH4 can't, nitrate has a much harder time passing through as well. However, it is not totally blocked, the result is that it takes much higher concentrations of nitrate and/or longer exposure times to have an effect on fish.
Without the nitrate in his tap, elmo's tank should have been doing fine. Plants consume ammonium so most of the total ammonia (TA) in the tank was likely being taken up by the plants and not bacteria. So this portion of the TA was not being converted to nitrate. Further, most plants want to take up nitrate which should act to lower any in the tank if not eliminate it. And if one is adding ferts with nitrogen (often in the form of nitrate to some extent) and then has lots of NO3 in their tap, it can build up.
I had indicate in some of the other threads in this topic that ro was likely the best solution. I felt it was a better solution than trying to us a nitrate reactor on the tank. It really is the tap water that is the problem here and one easy way to manage that is via dealing with it before it goes into the tank. One can do this in a number of ways. One is to mix ro and tap to get a resulting water much lower in nitrate. Another would be to hone one's mix of fertilizers to lower the nitrogen (nitrate) component because it is already in the tap.
Another way to deal with the problem could be a sump acting as a veggie filter filled with lots more nitrate sucking plants. Using SeaChem denitrate has its drawbacks. For one it requires a pretty slow flow rate (50 gph or less) which means separate equipment for if from the rest of one's filtration. Then, like any media, it can clog. What this media does is use other bacteria living on the outermost portion to use up the oxygen in the water passing through so what reached the anaerobic deitrifying bacteria in the center is devoid of O. To much flow will defeat this because the "outer" bacteria can nit use all the O that fast. Next, since this is a porous media, it can be clogged solids in the water. If it clogs the flow to the center is the first thing to slow and/or stop and this means the denitrifying process suffers as well.
Finally, the directions for this product state:
Q: How much nitrate will de*nitrate™remove?
A: It is recommended that if nitrate levels are very high that they be brought down to at least 20 ppm through water changes before using de*nitrate. At that point de*nitrate will bring the nitrate levels down to 4 – 5 ppm after several days of use. Since de*nitrate™, Matrix™,and Pond Matrix™are all biological support media, they do not actually ever exhaust, but they can grown less efficient with use by pore clogging. Prefiltering the water before it passes through these products will extend its useful life.
from
http
/www.seachem.com/support/FAQs/denitrate.html
But in the situation here the problem was/is nitrate in the tap.
Basically, the nitrogen cycle in our freshwater tanks is incomplete. The final step is not nitrate, it is the conversion of nitrate back into the very thing that begins the process, nitrogen. Since this is an anaerobic process for aquariums, and because there are other things that build up in tanks, we do water changes for freshwater. Sw folks have live rock and other goodies that can help handle nitrate so they are not saddled with having to do the same sort of water changing. But they have other issues they deal with that the fw side doesn't.
Given this is a planted tank and given that there is now ro water involved and denitrate too, I would become a bit concerned about a potential lack of nitrate in the tank and what that means for the plants and especially for algae. Despite what all the plant pros say regarding nitrate and phosphate not causing algae, they are wrong to the extent that when one has way too much of these things, the result will definitely be algae. There is a difference between the controlled dosing and control used by folks who know what they are adding, it is another thing if they double or triple the amount of phosphate and/or nitrate they are adding each time. Apparently, the situation here that is causing issues is not just some nitrate it is way too much nitrate coming in via the tap not via sensible fertilizing or bacterial creation.
Elmo, if your tap nitrate is as high as you are indicting. I would not drink your water and, for sure, would definitely not give it to infants or very young children. I would have been more inclined to use a combination or ro water and a change in the fertilizer components before I went to the denitrate. Since you have done so already, you will need to monitor the opposite end of things now. You need to insure you are not removing too much nitrate to the detriment of your plants. Of course all of this is being complicated by the lack of accuracy of the nitrate test kits. At best they can indicate the direction things are moving but not a real accurate level of absolute levels.
