Low pH high kH

[withanf]

Hi everyone. I'm working on getting harder water in my tank.  I'm using RO water with Seachem Alkaline Buffer and Equilibrium.  I'm trying to get a pH of 7-7.5.  I was away for a weekend recently, so the tank went 2 weeks without a water change.  Thought I'd test parameters before changing water, out of curiosity.  My gH was 8 and kH was 6, more or less as expected, and my pH was 6.6.  All tests were liquid API tests.  I did NOT expect to find a pH under 7 with the kH still so high. 

My understanding is the kH will buffer the pH quickly up to 7 or so, then more slowly towards and above 8.  How could my kH have remained that high but the pH so low?  I really don't know what to make of it.  

[Kirsten]

23 minutes ago, withanf said:

How could my kH have remained that high but the pH so low?  I really don't know what to make of it.  

Wild! You must have some strong acidifying elements in the water. What's your tap water's pH? Do you have a lot of like peat moss or bog wood in there? Do you do CO2 injection?

From how I understand it, KH "buffers" by basically raising the pH a certain degree. You could start above neutral, but acidifying elements could build up and bring the pH down, down, down even if the mineral content is still there. Or if your tap water is going through an acidic phase, the KH will only do so much to raise the pH.

Like, if you added crushed coral to a cup of vinegar (which would probably be an interesting experiment), it would still read as acidic, just maybe a little less so, and the minerals would still be there, though they'd probably start breaking down in a strongly acidic environment.

[withanf]

Right now I'm buying RO water and adding additives before each water change.  My tap water can come from 3 different sources, 2 of which are really soft, with the 3rd being more regular-soft, but enough of a difference to be a concern I think.  Going with the RO water and additives to keep my "source" water stable (in theory).

There's a good chunk of Malaysian driftwood.  I boiled it twice before it went in.  I am injecting CO2, so that could be a factor.  

If the alkaline buffer only helps bring soft water up a bit, is there anything I can do to get live-bearer friendly water?  

[Fishdude]

1 minute ago, withanf said:

Right now I'm buying RO water and adding additives before each water change.  My tap water can come from 3 different sources, 2 of which are really soft, with the 3rd being more regular-soft, but enough of a difference to be a concern I think.  Going with the RO water and additives to keep my "source" water stable (in theory).

There's a good chunk of Malaysian driftwood.  I boiled it twice before it went in.  I am injecting CO2, so that could be a factor.  

If the alkaline buffer only helps bring soft water up a bit, is there anything I can do to get live-bearer friendly water?  

Okay so RO water is clean but notoriously hard to keep "stable" for this very reason. I'm pretty sure the pH of RO water can and is often below 7 to start with. Have you considered using crushed coral to raise and stabilize the pH and mineral balance?

Also I think your pH now may be fine for livebearers depending on what you want live-bearing in there.

[withanf]

Yeah, the pure RO is definitely <7 pH.  I didn't realize it was hard to modify!

re: crushed coral, actively considering it, yes.  I'm thinking I'll put a bag of crushed coral in the filter, and keep pre-mixing the RO and buffers for water changes.  I assume this is necessary so that I'm not dropping pure RO water in at water change.  

I'm planning to go with guppies, no specific type (NOT starting with a $60-per-trio type).  I was hoping to get pH to 7-7.5, but if ~6.6 is ok then I'll consider moving on from concern to happy dance. 

[Fishdude]

12 minutes ago, withanf said:

Yeah, the pure RO is definitely <7 pH.  I didn't realize it was hard to modify!

re: crushed coral, actively considering it, yes.  I'm thinking I'll put a bag of crushed coral in the filter, and keep pre-mixing the RO and buffers for water changes.  I assume this is necessary so that I'm not dropping pure RO water in at water change.  

I'm planning to go with guppies, no specific type (NOT starting with a $60-per-trio type).  I was hoping to get pH to 7-7.5, but if ~6.6 is ok then I'll consider moving on from concern to happy dance. 

I don't know what's best for breeding purposes but for just regular healthy fish it'll be just fine. I do think I've read that livebearers prefer harder water (not an expert opinion!). I think a bag of crushed coral is the way to go though to prevent a pH crash when you add fish to the mix. The pH will trend downwards and I know without the calcium bicarbonate to buffer you could get a much lower pH than you want in a hurry. Hope it works out!