KH 5dkh but ph at 6.6?

[GreenTea]

just tested by KH yday and found out that its 6.6 w/o CO2 injection...

is this possible?

cos when CO2 is injected, the ph drops to only 6.2, from the CO2 table, i am confused how much dissolved CO2 is in my tank..

pls advice

[vinz]

I think you made a typo, got me confused until I re-read the title.

5dKH, 6.6pH -> 38ppm CO2
5dKH, 6.2pH -> 95ppm CO2

It's possible that your KH reading or pH is wrong. The hobby grade test kits can be very accurate or simply expired. Are your fishes showing signs of CO2 poisoning? If not, I don't think it can be that high.

Get some tapwater and raise the KH of this tapwater by a known value (with whatever you use to raise KH in your tank), test the KH and note the value. Raise the KH again by a known value and test again. Does the test kit reading go up by the same amount as you raised it? When doing this test, raise the KH by large values, like 10dKH, to get better accuracy.

What do you use to test your pH? If it's a pen or probe, have you calibrated it recently?

[GreenTea]

hi vinz,

without CO2 injection, my ph is at 6.6

my question is, is it possible for the ph to be this low when the KH is at 5?

[rocketshrimp]

It is possible if you have substrate that softens the water...peat moss? leaves? drift wood? spilled softdrinks? ...

Chances are, your measurement is not accurate. Tap water should be about 7.2/4+ thereabout..

[GreenTea]

It is possible if you have substrate that softens the water...peat moss? leaves? drift wood? spilled softdrinks? ...

Chances are, your measurement is not accurate. Tap water should be about 7.2/4+ thereabout..

i just recalibrated my ph pen this morning... maybe ill try again tonight. thanx

[loupgarou]

tap water in singapore can be soft or neutral at 6.8-6.9

[GreenTea]

what confuses me is that all along i assumed that having higher KH means automatically also having high PH... maybe i was wrong all along...

any inputs?

[vinz]

When do you measure the water without CO2 injection? If you do it just before the CO2 injection starts, that will give you the lowest CO2 (highest pH) reading. But then there's is no gaurantee that at that time, your CO2 levels are at ambient levels.

The point I was trying to make in my original reply is: Are your KH and pH test kits/tools accurate? Verify they are working properly before you start to worry about your tank values. Because if the readings are wrong, you won't be seeing the real problem. Stop focusing on your readings... find out if the readings are correct in the first place. If they are, then start looking for reasons why your pH is too low (possible agents listed by rocketshrimp above).

[GreenTea]

When do you measure the water without CO2 injection? If you do it just before the CO2 injection starts, that will give you the lowest CO2 (highest pH) reading. But then there's is no gaurantee that at that time, your CO2 levels are at ambient levels.

The point I was trying to make in my original reply is: Are your KH and pH test kits/tools accurate? Verify they are working properly before you start to worry about your tank values. Because if the readings are wrong, you won't be seeing the real problem. Stop focusing on your readings... find out if the readings are correct in the first place. If they are, then start looking for reasons why your pH is too low (possible agents listed by rocketshrimp above).

when i measured the value ph 6.6, its just before CO2 injection and 3-4 hrs after CO2 injection, it was 6.2.

thus i dont know if my CO2 level is correct according to the table..

and my ph pen and kh test kit are accurate..

thanks

[vinz]

what confuses me is that all along i assumed that having higher KH means automatically also having high PH... maybe i was wrong all along...

any inputs?

You are half right...

If you raise KH, the pH will rise too. I.e. if you raise the KH in your tank water to 8dKH, the pH readings will shift upwards too. But that does not change the amount of CO2 in the water.

[GreenTea]

okie... but now, what puzzles me is that pH is 6.6 before CO2 injection, assuming that my pH and KH readings are correct, how do i calculate my CO2 level when pH is 6.2 after injection?

[vinz]

when i measured the value ph 6.6, its just before CO2 injection and 3-4 hrs after CO2 injection, it was 6.2.

thus i dont know if my CO2 level is correct according to the table..

and my ph pen and kh test kit are accurate..

thanks

Ok, if you are sure... take a sample of your tank water just before CO2 injection in a clean bottle, cover and shake vigorously to expel as much CO2 (and other gases) as possible. Then open and let it sit for a day. This will allow the sample to equalise to ambient CO2 levels. Take a pH reading. Assuming ambient CO2 to be around 3 to 5ppm, you are looking for a target pH of 0.8 to 1.0 lower then this value to achieve roughly 20 to 30ppm.

I'm still trying to find out the ambient CO2 levels in water.

[GreenTea]

Ok, if you are sure... take a sample of your tank water just before CO2 injection in a clean bottle, cover and shake vigorously to expel as much CO2 (and other gases) as possible. Then open and let it sit for a day. This will allow the sample to equalise to ambient CO2 levels. Take a pH reading. Assuming ambient CO2 to be around 3 to 5ppm, you are looking for a target pH of 0.8 to 1.0 lower then this value to achieve roughly 20 to 30ppm.

I'm still trying to find out the ambient CO2 levels in water.

okie... will try that.. thanx alot!

[vinz]

tap water in singapore can be soft or neutral at 6.8-6.9

Mine is 8pH out of the tap, the last I checked.

[rocketshrimp]

I think the ph is slightly different across the country....maybe the piping contributes to the ph as the water gets pumped around. The last I checked...I remembered it was somewhat higher than the neutral state...above 7. I will check again.

Btw, I am using a PH pen (azoo brand)...what do you guys use? Whick is more accurate...pen or testkit?

[vinz]

Pen is much more accurate. But you must get a pH 7 and pH 4 (I think it's 4) water to calibrate it every few months or so. Most well stocekd LFS should have them... though stocks are short once in a while.

[bclee]

Greentea, if your KH and pH test kits/pen are accurate, chances is that you have other buffers in the water. If you have added things like peat, pH altering substrate (e.g. ADA aquasoil, peat containing soil) or even driftwood, they are going to affect your KH reading.

KH test kits are based on acid-base titration. You actually drop in acid to neutralise the carbonate in the water. At the end point, the indicator change colour and the volume of acid (number of drops) added will tell you the amount of carbonate(KH) in the water. However, when there is other buffers (usually weak acids like humic acids), the acid will also interact with these buffers. It usually take more acid to reach the end-point when there are other buffers present. Therefore, you will read higher KH than the amount of carbonate you actually have in the water. Thus, this will also gives you an extraordinarily high CO2 reading from the charts.

BC

[GreenTea]

Greentea, if your KH and pH test kits/pen are accurate, chances is that you have other buffers in the water. If you have added things like peat, pH altering substrate (e.g. ADA aquasoil, peat containing soil) or even driftwood, they are going to affect your KH reading.

KH test kits are based on acid-base titration. You actually drop in acid to neutralise the carbonate in the water. At the end point, the indicator change colour and the volume of acid (number of drops) added will tell you the amount of carbonate(KH) in the water. However, when there is other buffers (usually weak acids like humic acids), the acid will also interact with these buffers. It usually take more acid to reach the end-point when there are other buffers present. Therefore, you will read higher KH than the amount of carbonate you actually have in the water. Thus, this will also gives you an extraordinarily high CO2 reading from the charts.

BC

supposing what u said about buffers like peat are present in my tank,

how can i gauge my CO2 level assuming that im having 6.2 after Co2 injection?

[bclee]

Greentea, you can't use pH now to exactly gauge how much CO2 you have.

For me, I usually push the CO2 level up slowly daily. I observe my fishes and algae. IME, fishes like rasboras and shrimps are particular more sensitive to CO2, watch for these fishes and shrimps as you up your CO2. When the plants are growing reasonably well and algae (especially BBA) is under control, provided all nutrients are in place, the CO2 level are probably just right.

BC

[rocketshrimp]

I suggest that you try to find what the "co2 level" is from the chart before you inject. After you inject co2, check the level again. Do the difference...that should give you the actual co2. Assuming all being equal.

Logically, I think that would work....