Question about blending R/O and Tap Water

[pwsusi]

Hi,
I'm currently using R/O water and blending filtered well water to bring the conductivity up to 150 micro siemens. My problem is that the KH of the water is too low and I'm afraid of pH crashes. Here are my water parameters...

Direct out of the tap
pH – 7.8-.80
Conductivity – 300 micro siemens
KH – 5 degrees
GH – 10 degrees

Pure R/O
pH – 6.2-6.4
Conductivity – 14 micro siemens
KH – 0
GH – 0

Blended water that i'm storing for water changes...
pH – 7
Conductivity – 140-150 micro siemens
KH – 0 to 1 degree
GH – 3 to 4 degrees

Ideally I'd like to have the GH and KH around 2 degrees. But as you can see my GH is twice as high as my KH. So when i soften the water with R/O my GH is right where I want it to be but there is no buffering capacity. If I add more tap water i'm concerned my pH is going to shoot up. I have the same concern about adding baking soda to increase the KH. I should also mention that I've been adding just a little muriatic acid to the blended water to lower the pH from 7 to about 6.6

Any thoughts on how I can bring up my KH while keeping my pH down?

Thanks,
Paul

[Ardan]

Some have added crushed coral to the filter to help bring up the KH.
I believe April does this in Vancouver.


hth
Ardan

[Alight]

For your water, skip the muriatic acid. That's what's killing your KH. Measure the KH and pH before you add the acid.

Remember that the pH of your tank water with fish in it will quickly lower in pH, even with KH of 2-3, because of the nitric acid produced by nitrification and because of the small additional amount of CO2 the fish will add.

If you look at the tables, you cannot have a pH of 7 or under with KH of 2 if bicarbonate is your buffer, if you have the normal amount of CO2 in a bare bottom tank that comes from fish and the atmosphere.

OK, so I'll bet that if you change 50% of the tank water very day, and have a full load of Juvie or adult discus (1/10 gallon), that your pH will settle some where around 6.6 - 7, even if you do the water changes with your RO/well mix and add no muriatic acid, and this water's pH is about 7.6.

Adding the crushed coral will, indeed raise your KH, but it will also raise your pH. It will end up exactly where you were before you added the muriatic acid when your KH gets to 2.

Al Light

[pwsusi]

Thanks for the info. I measured the KH and pH before the acid and at 150 micro siemens the KH is 2 and pH is 7. Adding enough acid to bring the pH down to 6.5-6.6 lowers the KH to 0-1 (one drop using the test kit stays yellow so i don't know if that really means 0 or 1). So I think you're right...I should simply skip the acid. I will try that and see if that pH falls a bit when I add it to the tanks with fish. This is only for breeder tanks which are either 20s, 29s or 40s. Juvies get the tap water because it's too expensive for me to make that much R/O water and they seem to do fine in it.

As far as "the tables" you were referring to...can you send me a link to that information? I'd like to continue learning as much about water as I can.

Thanks,
Paul