pH and hardness question

[pwsusi]

I'm currently using R/O water blended with filtered tap water. I'm blending it so the water is about 125-130 micro siemens....GH is 4, KH is 2, pH is between 7.0 and 7.2 (need a new probe for my meter and my eyes aren't sharp enough to pinpoint the exact pH using the little test kits). I'm probably going to continue using the water as is because I know the pH probably doesn't matter too much with water this soft. But, I'd like to learn something here about water if i can because i can't understand why i can't lower my pH without killing the KH.

It seems like when I add enough muriatic acid to bring the pH down to where I want it, I'll check the KH and it is 0. If I add less acid the KH stays at 2 but the pH doesn't move or maybe it moves a little and then bounces back up.

So my question is - it MUST be possible to have a pH in the low to mid 6's while still maintaining some buffering capacity. How would this be achieved? Instead of using acid would i have to buy a commercial ph down product? If so, what chemicals are typically in those products to make them work so that you can maintain a low pH? Like i said, i'm probably not going to change my water because things are fine with the fish and like they say "don't fix something that ain't broken". But, I'd like to understand more about this if i can.

Thanks,
Paul

[pcsb23]

I'm no chemist Paul but I'll try and answer some of your questions. For any acid to lower the ph it must overcome the buffering to some extent (if not all??). There will be a point where the ph drops but there is still some buffering. Buffering is not as big a deal though if frequent and regular water changes are being done.

As for the commercial ph down products I would strongly advise against these. they are predominantly made up of Phosphoric acid, which is a weak acid and also leaves phosphates behind (I believe). They are also very expensive as you will need significant amounts to overcome the buffering and you run the risk of ph bounce.

I find that in my BB tanks which I typically run at very similar conductivity as you, ie 120 to 130 microsiemens, that they settle to a ph of 6.8, but I believe my KH is lower than yours (unless you rounded up!).

I would absolutely agree with you though about the if its not broken philosophy!

[Alight]

First of all, don't add anything to your water. It's fine the way it is.

Secondly, if bicarbonate is your buffer, and the cations are Calcium or Magnesium, and your CO2 is essentially zero, which it will be unless you inject CO2 into your tank it is IMPOSSIBLE to lower you pH into the low 6 range without having less than 1 for your KH, unless you add CO2.


You can get a higher KH if you set up a different buffering system, say phosphate buffers, MEPS, MOPS, or other systems, but it won't work with bicarb. Check out the link below for why this is so.

http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

[pwsusi]

Thanks to you both. Also, that is great article...it explained a lot. Based on the calculator they have though it sounds like my CO2 levels are actually too low. None of my tanks are planted so i guess i shouldn't worry about that.