Newbie Question: CO2, pH, KH - The Planted Tank Forum
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post #1 of 3 (permalink) Old 11-04-2012, 01:09 AM Thread Starter
Join Date: Oct 2012
Location: Canada
Posts: 2
Newbie Question: CO2, pH, KH

Hello to all.

I've kept aquariums in the past before but this is my first try at a planted one. I've decided that I was going to give a DIY CO2 system and got everything I needed: dry ferts, water testing kits and a drop checker I got from eBay.

I decided to try the drop checker before I try anything first. Just to see where it's at. So the checker turns yellow which means too much CO2???? (Remember, I haven't done anything yet.) Ok. Maybe it inacurate. So I'll test the tap water's chemistry. I have a regular pH and a high pH tests. The reg. pH gives me 6.8 and the high gives me 7.8. Now if both gives me a result, which one do I know is the right one? The KH gives me 7. According to the pH vs KH table, 6.8 pH gives too much CO2 and 7.8 pH gives too little?

I'm confused.

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post #2 of 3 (permalink) Old 11-04-2012, 01:19 AM
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Join Date: Sep 2010
Location: Greensboro, NC
Posts: 4,729
First, your test kit is bad. That it's giving you two separate readings means it's off. Most common is probably the API Freshwater Master Test Kit, and there's a batch month and year printed on the bottles. After 2 or 3 years, it's time for a new kit. Though, on second thought, read and re-read the directions on the test kit to make sure you're doing it right. And test your tap water in comparison.

Secondly, your pH can be affected by several things in your tank, from substrate to filter media, so the pH/KH chart may be inaccurate, depending on your setup.

Thirdly, if you don't use 4dKH water in your drop checker, the drop checker is useless. Search here for 4dKH or drop checkers, and check Evilbay for 4dKH water. In all likelihood, the directions for the drop checker say to use tank water. They lie. Seriously.

And, finally, unless you have extremely sensitive fish in your tank, pH level is generally a non-issue. Many of us haven't bothered with checking pH levels in months, or even years (probably more than a year, for me). Further, pH drops due to CO2 injection are definitely a non-issue (the fish and plants just don't care), unless you have pressurized CO2 and use a pH monitor to turn CO2 on and off.

Good luck!

Last edited by kevmo911; 11-04-2012 at 01:22 AM. Reason: Goodly grammar is importantly!
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post #3 of 3 (permalink) Old 11-04-2012, 04:41 PM
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Join Date: Jan 2010
Location: Contra Costa CA
Posts: 11,721
I'm confused.
Me too.

With that high KH I would expect the pH to be above neutral, but if you have peat moss, driftwood or other organic matter in the tank the pH could easily be lower.

If the pH is in the range tested by the high range kit, then using the low range kit will show the highest possible reading it is capable of.
If the pH is in the range tested by the low range kit, then using the high range kit will show the lowest possible reading it is capable of.

API pH test kits overlap
low range tests the pH up to 7.6
High range tests the pH down to 7.4

If your pH really is in that 'in between' range (7.4 to 7.6), then both will test correctly.
If the pH is outside that 'in between' range then one will report that 'in between' result, and the other is the correct pH.

It is odd that both give you results that are outside that 'in between' range.

Test some other things such as tap water, then tap water with a pinch of baking soda added.
Run some tap water in a glass or jar and let it sit out overnight, test again.
If you have any distilled or reverse osmosis water in the house, test that, too.
If you are getting different numbers for all these, then the pH tests are responding to something different in the water.
The KH test ought to rise when you test the water plus baking soda.

The other thing to remember is that hobby level test kits are not lab quality. Your pH and KH tests might be off.

I sure would double check the water in the DC. It ought to test 4dKH. If it does not, then look here to find out how to make 4dKH water.
Test several of the stages to see how your test kits respond.
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