[JoelB]

I have a fairly new NPT which I gave a 75% water change two days ago. My tap water is very soft. I've now measured a few dkH and it is mostly carbonate hardness. I suspect it is leeching from my soil substrate. The pH stays around 7.3

Does this suggest anything about how it is forming and how I can counteract it?

 

[lauraleellbp]

Why are you feeling the need to counteract it?

 

[Hoppy]

All KH is carbonate hardness. What is a "few dKH"? A great KH to have would be 3 dKH, which is certainly a few. But, isn't 10 dKH also just a few?

Anything in the tank that contains carbonates, calcium carbonate for example, will add carbonates to the water as it slowly dissolves. So if your substrate contains any carbonate rocks like limestone, or if you have rocks as part of your aquascape and they are carbonate rocks, you will see a slowly rising KH. I doubt that it will ever be a problem since you apparently do change water periodically.

 

[JoelB]

As in 4 or 5. In my original post I meant to say GH but I can see it makes no difference now.

In my experience plants will stop growing when my water gets too hard, though this I have noticed with non carbonate hardness. I'm yet to prove it it going up infinitum... but at this rate (and limiting to 25% water changes as I will if I put in some fish), I'm concerned I would have to do water changes every second day. So I'm concerned about stability and the the lack of natural balance.

 

[MoonFish]

PSA:

Plants grow in hard water. Are you feeding the plants at all?

 

[Hoppy]

GH is good for plants. They need the calcium and magnesium and there is no limit on how much you can have, within reason, of course. Too high a KH can be a problem for some plants or fish.

Fish do fine with 50% or greater water changes. In fact those who do the Discus thing routinely change that much water every day or two. I think you probably don't have a problem worth worrying about, but I agree that it is always best to ask if you aren't sure.

 

[lauraleellbp]

Oh wait- this is the tank with compost & potting soil substrate, isn't it. Hoppy- he's trying to work towards a no water change Natural Planted tank, but having some serious organic decomp issues in there, that's why he's doing the large water changes now.

If it's your gH rising it may be from some additives the manufacturer put into the potting soil.

I wouldn't expect stability in this tank until the organics (especially the manure) finish breaking down.

 

[JoelB]

laurel, My dkH tested the same as GH, as best as I can read it so this is all carbonate hardness. The mixes I purchased were organic with nothing added. The compost includes worm castings and the assistant told me it was all natural, well broken down and had a neutral pH.

Moonfish and Hoppy, I had a previous tank where I used to mineralise the water with mag and cal during water changes. This tank stopped growing on me once despite it having all the ferts it should have needed. I read an article about hard water being a problem and so I measured and found GH over 15 not including the kH component of 3. I did a 75% WC and the tank took off and grew well for two weeks without doing anything else to it.

 

[lauraleellbp]

A neutral pH when dry doesn't mean it's going to remain neutral once wet and decomposing.

 

[MoonFish]

Moonfish and Hoppy, I had a previous tank where I used to mineralise the water with mag and cal during water changes. This tank stopped growing on me once despite it having all the ferts it should have needed. I read an article about hard water being a problem and so I measured and found GH over 15 not including the kH component of 3. I did a 75% WC and the tank took off and grew well for two weeks without doing anything else to it.

You only measured one thing but when you change the water, you add many things. Plants grow in hard water.

 

[Hoppy]

This isn't really relevant, but KH isn't a component of GH. GH is essentially ppm of calcium and magnesium, while KH is ppm of carbonate. I have no experience with Walstad type tanks, so I have no ideas about this problem.