Water Chemistry Queries

[corymad]

Hi All

We live in the UK and our tapwater has a lot of nitrate. Consequently we effect 10% water changes weekly using two thirds remineralised RO water and one third tap water.

I think I need to add some sodium bicarbonate to increase the KH without effecting PH or GH and am a bit worried about adding this with catfish in the tank. Will it be OK to add sodium bicarbonate?

Background info

RO water plus JBL aquader remineraliser (plus one third tap water) gives KH 3, GH 6 and PH7.5
Tank is at KH2, GH6, PH 6.8 - BUT KH keeps disappearing and dropping (being used by plants?)

Within 2 days timespan , tank KH has dropped to less than 1 degree KH!! Have tried adding extra Aquader but KH continues to drop ( whilst GH rises due to the extra Aquader)

Many thanks for any replies

 

[iggy01]

It's safe to use bicarbonate of soda to raise KH.

1/4 tsp will raise the KH of 50 litres of water by 1 dKH. However, it will also raise the pH slightly also.

Could there be some other acid in your tank eating into the KH? Have you recently added any bogwood?

 

[Bloo]

What is your tank and tap nitrate readings ? Do you really feel it neccesary to use RO water on a general community tank ? Here in (and around) London we probably have some of the harshest water and still successfully keep community fish.

The kH shouldn't be affected by the plants at all. I have a fully planted tank and the kH never changes by more than 1.

With your kH that low, it will mean that your pH constantly swings as well - really not good for the fish at all.

 

[corymad]

What is your tank and tap nitrate readings ? Do you really feel it neccesary to use RO water on a general community tank ? Here in (and around) London we probably have some of the harshest water and still successfully keep community fish.

The kH shouldn't be affected by the plants at all. I have a fully planted tank and the kH never changes by more than 1.

With your kH that low, it will mean that your pH constantly swings as well - really not good for the fish at all.

Tap nitrate is at least 20 ppm, often more. We've had tank nitrate levels of 80 ppm and above weekly but with two thirds RO and one third tap water effecting two 10% water changes weekly (using RO / tap mix) we can get nitrate down to less than 20 ppm. The reason that we're messing trying to improve water quality is twofold - firstly the tank is suited to South American species which prefer soft acid water and secondly, were hoping to move some of the catfish and community fish into a 180 litre tank and use the 260 litre tank for discus.

The tank has a sandy substrate and lots of bogwood. We've just bought some JBL substrate and are using that in shallow pots (about three quarters of an inch deep) to see whether plant growth improves.

We've also tried running aquatic peat through an external filter to soften the water, but this seems a little hit and miss re acuracy of results. PH seems stable at 6.8 but think we'll have to increase KH to about 4 to keep system stable.

 

[iggy01]

Too much bogwood in a tank can play havoc with water chemistry. This may be the cause of the falling KH.

Some people can have lots of bogwood in a tank and not have any problems, others can have different experiences.

 

[andywg]

20 ppm nitrates is fine for FW tanks. 100ppm is the point where you have to really worry about nitrates.