Change of filter media to all foam has affected nitrates unexpectedly !!!

[hamfist]

Roughly 5 months ago I changed all the filter media in my 3 x canister filters on my 130g tank to all foam. Previously having had a bit of foam but mainly Seachem matrix and other ceramic media in them. THis tank had not been having any problems but I had been convinced that all foam was at least as good if not better than specialist media. Anyway, the tank has continued to very effectively clear all ammonia and nitrite - no problems. Just FYI, the tank has no real plants.
The tank had previously run at a very steady 20-30 ppm nitrates. My tank maintenance and water change schedule has not changed. The fish load and feeding is pretty much the same. However ........ and here's the punchline ....... now with the all foam media the tank is running at <5 ppm nitrates. Whats going on ? Its great, but I don't understand how this can happen unless somehow I have created anaerobic areas within the foam which has become a nitrate reactor. I am certain that nothing else has changed in the tank except the change of filter media. Has anyone else experienced anything like this ?

 

[esoxlucius]

Anaerobic pockets are usually linked with deep beds of substrate where water movement is virtually non-existent. Quite the opposite to what's going on inside a filter, so I doubt it's that.

I also doubt a change in filter media is the answer as filter media doesn't get rid of nitrates, whichever media you're using, though some do claim to do just that!!

Maybe a discrepancy with your testing kit? Maybe your water source had nitrates in it, but your water authority have improved?

Whatever it is, don't worry about it, it's a nice dilemma to have!

 

[hamfist]

Anaerobic pockets are usually linked with deep beds of substrate where water movement is virtually non-existent. Quite the opposite to what's going on inside a filter, so I doubt it's that.

I also doubt a change in filter media is the answer as filter media doesn't get rid of nitrates, whichever media you're using, though some do claim to do just that!!

Maybe a discrepancy with your testing kit? Maybe your water source had nitrates in it, but your water authority have improved?

Whatever it is, don't worry about it, it's a nice dilemma to have!

I'm certainly not worried, just puzzled. My water source has been remineralised RO for years, so zero nitrates going in there. My substrate is an inert gravel and gets completely disturbed during the water change, weekly, so no anaerobic pockets there. I am completely stumped as to what is going on. Pleased, but puzzled.

 

[Cal Amari]

I agree changing the media itself doesn't explain nitrate drop, as the media itself doesn't affect nitrate. Unless the old media had clogged pores, buit up slude and gunk that was constantly decaying and releasing nitrates, a reason some on here dislike canisters. The foam media will eventually do the same unless regularly rinsed and or replaced, as sludge and gunk build up over time. This isn't the media itself though, just the trapped detritus and poo.

 

[duanes]

I alsi use foam,in tandem with heavy plant filtrarion.
And never see detectable nitrate.
Like esoxlucius (and according to Swiss Tropicals) the anoxic (semi-anerobic) areas create pockets that reduce nitratenaturally.

 

[danotaylor]

There’s nothing about your system that can account for what you are seeing.
Is your test kit past is expiry date?

 

[hamfist]

There’s nothing about your system that can account for what you are seeing.
Is your test kit past is expiry date?

No its brand new and tests on other tanks are what I would expect. The test kit is good.

 

[hamfist]

Thus .... I'm still convinced that the big drop in nitrates I have experienced in this tank is down to changing to having 20 ppi foam only in all canister filters. Absolutely nothing else has changed, not even food brands. This tank has been running for many years.
For the sake of complete transparency the only other change is that I have added another 12 x Congo tetras (which, if anything, should increase nitrate levels slightly) since I last measured nitrates at around 25 ppm.

Logically the explanation must lie in enough of the filter media getting clogged up with mulm in such a way that it becomes anaerobic and starts removing nitrate. I'm just so surprised by this as I rinse this foam roughly every 4-5 months - although it is pretty clogged by rinse time.

 

[jjohnwm]

I've read a great many articles on this idea of anaerobic filtration being used as a nitrate reduction mechanism...and all of them claim that those "anaerobic" bacteria utilize the nitrate as a source of oxygen, rather than nutrition. The bacteria split the nitrate ion to access the oxygen in it...nitrate is NO3...but they still require an energy/carbon source such as sugar to provide them with "food". All the fancy-shmancy nitrate-reducing filters that the techie-aquarists construct to relieve themselves from the horrendous task of simply changing water have some sort of injection system to introduce vodka or a similar source of carbon into the water to keep those bacteria healthy and happy.

Assuming that's true...how on earth can an aerobic zone in your filter be helping you if you are not also providing those bacteria with a food source? This isn't the first time I've seen this claim being made; as opposed to nitrate-reducing filters that are designed and constructed specifically for that purpose, this miraculous disappearance of nitrate seems to occur without an easily-visible explanation, and the idea of accidental anaerobic zones is often brought forth as the answer.

Which school of thought is correct? The mad scientists who aim for this goal and sometimes achieve it...or the "normal" aquarists who can't explain the phenomenon any other way? Beats me; I'd really love someone to lay it out in black and white.

In the meantime...relax and enjoy it.

 

[esoxlucius]

Being a bunch of tinkerers, which basically is what us hobbyists are, I can see why people go to great lengths to try and set up new fangled systems to deal with certain issues.

I've also read a lot of stuff regarding nitrate reduction, most of which I simply don't understand, and the vodka dosing thing is one of them, lol.

Trying to get your head around a complex idea such as this is one thing, putting it into practise in a successful manner is another.

Especially when you needn't have bothered in the first place! Just do a water change, far less taxing on the old grey matter, lol.

But again, I can't be too harsh on people who try it because it brings us back to the tinkerer thing, and one thing we love to do as hobbyists is tinker about.