KH kit measurement

[AquaObsession]

Hi,

I am not sure of the relevance of this post in this forum (fertilization and algae)...but I post it here due to the relevance to Co2 ppm... Moderators feel free to move my post...

Anyone can recommended a good KH measure kit? I am currently using the "sera KH kit which gives me a reading of 1 or 2. I suspect the accuracy of the readings?

anyone using other brands or methods which are proven to be reliable? (accurate)

Thanks in advance..

[dc88]

Hello,

May I know why you need more precise KH reading than the typical test kit provided ?

I had tried Dupla, Sera and Tetra before and they all work about the same by counting the drop into a fixed sample volume that turn from blue to yellow. That is generally good enough for determining teh CO2 level (combining with the PH reading).

By the way, I learnt from the APD mail list that the common KH-PH-CO2 table (that available in many reference source) only apply to a tank water where the bicarbonate is the main buffer of the water's alkalinity. If there are other staff in the water (such as PO4 due to e.g. too much fish food) than it may gives a false reading.
One way to "calibrate" the reading is to take some tank water in an opened container and leave it overnight at a opened area (to allow its CO2 level equalize with the atmoshoere level of ~3ppm CO2) then check the PH of this sample water and from the KH-PH-CO2 level find out what would be the KH reading giving the PH reading you measured and at 3ppm CO2, this will give you a reference KH number. Then use this reference KH number and the tank's PH level to find out the "real" CO2 level of the tank. This method will remove the factor due to the other staff in the water than affect its KH value other than the effect by the bicarbonate.

[valice]

One way to "calibrate" the reading is to take some tank water in an opened container and leave it overnight at a opened area (to allow its CO2 level equalize with the atmoshoere level of ~3ppm CO2) then check the PH of this sample water and from the KH-PH-CO2 level find out what would be the KH reading giving the PH reading you measured and at 3ppm CO2, this will give you a reference KH number. Then use this reference KH number and the tank's PH level to find out the "real" CO2 level of the tank. This method will remove the factor due to the other staff in the water than affect its KH value other than the effect by the bicarbonate.

I believe that this is a good piece of information for everyone. But it is abit late and brain not really working, so could you explain it further?

So after how do we use the "calibrated" kH value to check the actual value of the CO2? Attenuate the kH we measured from a fresh tank water or what?

[vratenza]

no wonder my CO2 is measuring 60PPM based on my KH kit and pH meter...... my fish and shrimps are not dying........but my algaes seem to be thriving despite large amt of ferts and reduced lighting..... so i guess my CO2 is not high enuff still....

I am using seachem onxy (which purportedly raise the KH by a few degree) and also i have been dosing KH2PO4........

[dc88]

I believe that this is a good piece of information for everyone. But it is abit late and brain not really working, so could you explain it further?

So after how do we use the "calibrated" kH value to check the actual value of the CO2? Attenuate the kH we measured from a fresh tank water or what?

Yes, which means you don't need to measure the KH at all. Just measure the PH of the sample water that sit for some time to equalize its CO2 with atmosphere to a known ~3ppm CO2, read the would be "reference KH" from the CO2 table, then measure the PH of the tank water, use that "reference KH" to find the CO2 level.
This method also save you money to not have to buy a KH test kit ! A PH test kit will be all you need.

[PeterGwee]

Yes, which means you don't need to measure the KH at all. Just measure the PH of the sample water that sit for some time to equalize its CO2 with atmosphere to a known ~3ppm CO2, read the would be "reference KH" from the CO2 table, then measure the PH of the tank water, use that "reference KH" to find the CO2 level.
This method also save you money to not have to buy a KH test kit ! A PH test kit will be all you need.

Be careful.....if your KH is very near zero or zero, the pH/KH relationship no longer holds nor does a normal pH pen probe measure pure water.

Regards
Peter Gwee

[dc88]

I refer to the situation where there is more than bicarbonate in the water that buffer the PH (e.g. if dosing PO4 or too much fish food, etc) the normal KH/PH/CO2 relationship need to be adjusted. (usually encountered as unusally high KH reading that showed a CO2 level way over 30ppm while fish in the tank still behave normal) Hence the method suggested here to measure PH of a sample of water from the tank left aside for some time to equalize with ambient CO2 level (typically 3ppm) and calibrate the "would be KH". Or simply just measure the PH of the tank vs. the PH of the sample (with known Co2 level) will help to find the real CO2 level. Of course the tank will not have the PH crash situation since the buffer is high in the begining.

[PeterGwee]

Yes, double check on that as always to be sure for CO2. A pH difference of 1 should more or less give you ~30ppm from a tank water sample left 24hrs out to equalize with the ambient CO2 surrounding it. The other thing is to make sure your CO2 rate is consistent from the start to the end once it comes on as well as the responsiveness of your CO2 system to get the CO2 into the good range within an hour after coming on.

Regards
Peter Gwee

[dc88]

OK, I did the verification last night :
- water from tank measured as : PH=7, KH=5 (from the CO2 table about 15ppm CO2).
- tank water sample took from last night, left open-air and measured this morning : PH between 7.5 to 8 probably closer to 8. (using Sera PH test kit that can only tell a 0.5 PH increment) which is roughly the range of atmospheric CO2 level of 2~3 ppm. Forgot to check its KH ... some said that KH should be unchanged in this case. (I will repeat the test again to include KH measurement of the over-night's sample.).
If its correct, the reading can be implied as the tank water is prodominatly buffered by bicarbonate and likely low level
of PO4 ?
One caveat of this method is that you need a more precise PH meter and only know the CO2 result in a longer lead time.
I guess my recommendation would be : still use the normal PH/KH method unless you get very weird CO2 reading (liked extremely high CO2 even you did not inject a lot) then you double check with this "Tank's PH/Sample-over-night's PH" method.

[PeterGwee]

OK, I did the verification last night :
- water from tank measured as : PH=7, KH=5 (from the CO2 table about 15ppm CO2).
- tank water sample took from last night, left open-air and measured this morning : PH between 7.5 to 8 probably closer to 8. (using Sera PH test kit that can only tell a 0.5 PH increment) which is roughly the range of atmospheric CO2 level of 2~3 ppm. Forgot to check its KH ... some said that KH should be unchanged in this case. (I will repeat the test again to include KH measurement of the over-night's sample.).
If its correct, the reading can be implied as the tank water is prodominatly buffered by bicarbonate and likely low level
of PO4 ?
One caveat of this method is that you need a more precise PH meter and only know the CO2 result in a longer lead time.
I guess my recommendation would be : still use the normal PH/KH method unless you get very weird CO2 reading (liked extremely high CO2 even you did not inject a lot) then you double check with this "Tank's PH/Sample-over-night's PH" method.

Ditto to what dc88 has said. Nutrients are easy to take care via the EI method. CO2 is always difficult and folks should focus on it rather than messing around with nutrients which are less subtle.

Those pH test kits with 0.5 intervals are the worst...you can guess better than that. You would need something more precise like a pH pen/monitor to get close.

Regards
Peter Gwee

[dc88]

Hi Peter

Any recommended source of PH pen locally ?

[PeterGwee]

C328, ACEZ at sim lim tower and most LFS stock pH test pens imo. If you want hight end ones, those miniLabs pH test pen (ISFET pH sensor) from Hach (they have a local distributor at Bukit Batok) comes to mind.

Regards
Peter Gwee

[bclee]

For even higher end ones, you can send your water samples to my lab for analysis. For a just over a couple hundred dollars, I can perform a NO3-, NO2-, SO4-, PO4--, Mg++, Ca++, pH and alkalinity.

Ok... seriously, if you consider the accuracy of ±1° accuracy of KH kits and ±0.2 accuracy of pH pen, you will be expecting about ±10~20ppm error in CO2 concentration. Therefore, unless you have a extremely good method to test for CO3-- concentration (not just KH), a good hobbyist pH pen would probably suffice.

The pH drop method is a pretty good way of estimating CO2 concentration. However, the errors in CO2 concentration would probably be just as large.

For me, I have given up testing years back. I just ask my fish (or shrimps or others...)... ... I simply push the CO2 as high as possible without causing distress to the fish (or shrimps or others...). Add in good circulation... and your plant CO2 need should be met quite sufficiently.

BC

[PeterGwee]

Yes, but using those kits to get close is useful before tweaking it further rather than getting lost in the park.

Regards
Peter Gwee

[bclee]

Yes, but using those kits to get close is useful before tweaking it further rather than getting lost in the park.

Regards
Peter Gwee

On the contrary, it was the pH/KH readings pointing 100+ppm that kept me going round in circle until I realise that the pH/KH readings are out most of the time.

Just note that most of the time chances is that pH/KH readings usually overestimate the CO2 concentration.

BC

[dc88]

Hi

I repeated the test on measuring the tank water PH/KH (last evening before lights-out) and this morning (sample water left opened air overnight).

First Reading : PH=7, KH=5, => CO2 = 15ppm from table
Second Reading : PH =8, KH between 5 and 6 => CO2 ~=1 ~ 1.2ppm.

I guess this brought up 2 points :
- KH will change as well. So the assumption that "the KH of the water sample left over-air to equalize CO2 with ambience is constant" is not true althought the changes is small (1/2 degree DH in my test).
- CO2 level in atmosphere is also fluctuate.

Bottomline, all these are just estimation. I concur with bclee's comment above. I think as long as plants and fishes are doing well and have some ball-part of buffer in water (KH > 4) while injecting CO2 we should not be too hung up on measuring CO2 level.

[PeterGwee]

Some folks have CO2 response issues (unable to get the CO2 in good range within an hour) and the idea of telling them to crank the CO2 till fish show distress before backing off would be disastrous (their chance of killing fish is great).

Regards
Peter Gwee