Acidic ph and filtering.

[catmar]

Had a chat about this elsewhere and was never completely satisfied with the outcome (there wasn't one.) Is it neccessary to biologically filter using acidic water? Assume water is <7 and stable there. Could the build up of ammonium be controlled with w/c, avoiding nitrite.nitrate.

[MatsP]

Yes, you still need to have biological filter, even if the pH is low - ammonium and ammonia are both toxic to fish, and further, there will still be SOME ammonia even at low pH - it just is less of a proportion of the ammonia compared to ammonium. If you have no biological filtration, ammonia will build up, and eventually become levels that are killing your fish - low or high pH - it just happens SOONER at high pH.

Of course, if you run enough water through your tank, ammonia levels won't reach dangerous levels - say you do about 100% water change each day (in portions throughout the day, or you'll still get a buildup between water changes), you would probably be OK - but the number may be 200% or 300% depending on stocking levels, of course.

And further, I don't think you will avoid nitrite - the ammonia eating bacteria will eventually establish to some extent in your tank, and once you have nitrite levels turning up, there will be nitrate producing bacteria forming in the tank.

--
Mats

[Bas Pels]

Besides, what's wrong with nitrate? It's by far the least tocix compunt in the whole nitrogen-waste system

On a side-note, where there is ammonia (or whathever follows next) there is also phosphate, micro pollutants and, I think quite important, pheromones - all detrimentous to your fishes health.

[catmar]

The thought was prompted by a visit some time ago to a well respected lfs. I had an ammonia spike and was asked what the ph of my water was, this being c6, they told me that in acidic water I would have ammonium, which was virtually non toxic. If this is correct, I wondered why filter at all in water @ <7, just change water as normal to prevent build-up of Ammonium. I have heard of people keeping Apistogramma at low ph without filters and regular w/c. Have to say I'm not convinced at all.

[MatsP]

The Ammonia/Ammonium balance does depend on pH, but if your pH is around 6, then there will be 100 times more H+ than OH- ions. But there won't be 0 OH- ions (it would be CLOSE to zero if your pH is say 2.0 or such - but this would be pickled/rollmop herrings, not fish in an aquarium).

Of course, if the pH is, say, 4.0, the H+ is 1000000 times more than the OH- ions - this will lead to extremely low levels of ammonia. But this is also pretty hard to keep stable and many fish won't like that low a pH over a longer term. There will be VERY little ammonia in this water.

[the calculation of the OH- and H+ ion levels is "take a one and add two zeros per each level below seven" - at pH level, the balance of H+ and OH- is equal.]

"no filtration" is probably not true - the tank will still have bacteria in the tank, just not in a filter container. The gravel, leaves of plants, etc, etc.

--
Mats

[catmar]

Appreciated, thanks all.

[wrasse]

catmar, you mentioned apistogramma keepers... these fish don't produce much waste and they aren't messy feeders. They are often kept in species-only tanks, so - low population. They are also quite fussy in that they prefer live/ frozen live foods which I would imagine once it has been digested and passed through the fish, results in far less mess than dried foods.
As Mats says... the plants and background bacteria in a tank together with water-changes takes care of water quality issues.