How low can pH go woth DIY CO2

[bman]

I hooked up a DIY CO2 bottle yesterday in my 20 gallon tank. Starting pH was 7.2; this morning it reads 6.8. How low can I expect the pH to swing?

I do not know my KH reading yet. Going out today to possibly get one, but do I really need one? I work for a pool store and I am going to bring a sample in to test for total alkalinity and calcium hardness

Would this be enough, or should I spring for the KH kit (if I can find it)

 

[Glenc]

You should get a KH kit as KH is the buffer that allows you to inject CO2 safely. If your KH is below 3, your PH will crash, fish can and will probably die. How long have you been injecting CO2? If it's been a week and your PH is steady at 6.8, you are probably ok. Then again, that depends how much CO2 is actually being absorbed into your water. PH drops pretty quick if your KH is low. You also need to know your KH level so you can measure how much CO2 you are actually injecting. Just for piece of mind, I would get the kit.

 

[Glenc]

Sorry bman, says you have only been injecting for a day.

 

[Thebluyak]

my PH swung really low, went from 7.2 to 6.6 then to 6.2. I need to get a KH test kit but its been holding steady at that PH

 

[fish_4_all]

Mine went from 7.2 to 6.6 and has stayed there but my KH is really high, 9-11 dKH on a regular basis.

 

[czcz]

bman, KH shouldn't change much unless there's limestone or something in the tank. Suggest you just test it at work now, in a few days, sometime later, and then occasionally, assuming your test results make sense.

As far as I know Ca won't affect CO2, at least on any significant level, by the way. (It along with Mg is GH.) Doesn't hurt to know Ca though.

 

[Reechard]

FYI the pka of carbonic acid is 6.36 roughly. Your swing down to 6.2 is about as low as it will go unless you dump vinegar in or something. Your KH will affect this as the CO3 buffers the pH and will keep it from creeping too low which is why fish_4_all's pH only went down to 6.6.

 

[bman]

OK thanks to all for your responses,

BUT

I have a test kit for a swimming pool that measures TOTAL ALKALINITY in ppm. What is the significance of that to Carbonate Hardness? They sound very similar, if not the same. Total alkalinity in the pool is a buffer for pH.

I have brought home the kit and will post the alkalinity after I test it in a few minutes. I'm thinking it should be around 50-80.

It's not that I am too cheap to buy the KH test kit, I am just making an assumption that KH and ALK are the same.

 

[Lonewolfblue]

FYI the pka of carbonic acid is 6.36 roughly. Your swing down to 6.2 is about as low as it will go unless you dump vinegar in or something. Your KH will affect this as the CO3 buffers the pH and will keep it from creeping too low which is why fish_4_all's pH only went down to 6.6.

Are you sure 6.36 is roughly as low as it will go when injecting CO2? I have a pressurized CO2 system and have no problems driving mine down below that. I keep mine roughly 6.2-6.4, but I've driven it to 6.0 with no problems at all, and would probably go lower if I set my controller lower. Anyone with more experience please chime in on this. Thanks...

 

[fish_4_all]

Check Here.

It can actually go quite low, the site says as low as 4.37 so KH is very important as a stabelizer. I don't pretent to understand it all but it does give something to think about.

 

[bman]

Tested the Total Alkalinity and it was 100 ppm. In the pool world that is an ideal reading, meaning that there is plenty of buffer for the pH to remain stable.

For now, I am happy with that figure, but will probably get a KH test kit when I return from my weekend vacation trip. I will have to see what is the difference in testing is, and if it's the same I will feel like a shmuck for buying a test kit I could get from my work for free!

 

[czcz]

I am just making an assumption that KH and ALK are the same.

You're correct.

FWIW, I have similar KH from tap -- 100-120ppm, 5.5-6.0 dKH -- and grew practically whatever I wanted in it with DIY CO2, so I agree you'll be fine. Just need additional testing to verify it doesn't change to much. If it does change, then a KH test will almost certainly be necessary for the troubleshooting process.

HTH