Water Quality problems.

hi guys.

i am having some problems maintaining the water quality in my tank.

i have 4 ax's, in a 140 litre tank.
the tank is filtered, cycling 300 litre per, has aeration, small gravel, sponge filter, ammo-lock carbon and a normal carbon bag, no 'live' plants, no moss build up, no food left in the tank, all 'visible' poo removed, 30 litres of water changed weekly,
the Ph varies daily, it can go as low as 6.2 and i can get it back to 7.6 after about 3 days of gradually bumping it up. i check the pH via 2 different kits.
the ammonia is less that 0.25ppm and despite water changes and Ammo-lock carbon and ammonia binding additives, the ammonia persists at <0.25ppm.
the NitrITE is and has always been 0ppm.
the NitrATE ranges from 5-10pmm but has jumped to 40ppm today (did water change yesterday).
the Carbonate Hardiness is constantly <20ppm.

can anyone see anything obvious that i have missed in maintaining the water.

the water always appears clean and clear and the ax's behaviour and appetite are very good. they all had a 'touch of the fungus' around December/January but have all recovered well and have regenerated gills, lips, fins, tails and toes.


anyone got any ideas???

peter

my first guess would be thet there is something going on with your bacteria colony, causing the fluctuations. Try adding a product called Cycle (made by Hagen), and some Bio-max (also by Hagen under the Fluval brand) to your filter if possible.

Also, when was the last time you changed your ammo-lock?

Have you read all the instructions/cautions that come with the ammonia binding additives you've using? Quite often they'll cause false positive readings when you test for ammonia. It should say which test kits are incompatible..

What do you mean by "i can get it back to 7.6 after about 3 days of gradually bumping it up"? If you are using those "pH UP" and "pH DOWN" solutions to alter the pH, please stop! This is the entire reason for the fluctuation.

A pH of 6.2 is very close to neutral and nothing to worry about. Given your low hardness and slightly-low pH, I suspect you live in an area with soft water. If you want to raise the pH, add limestone, crushed coral, or calcium carbonate sand to the tank. This will make the water a bit harder and a bit higher pH, but without causing fluctuations. But really you do not NEED to do anything to the pH if it is naturally 6.2.

Regarding the ammonia and nitrite, I would guess that they will even out to zero as soon as the pH is stable.