failure of kh/ph/co2 ratio

[lip]

I believe that the presence of non-CO3 buffer in my tanks have skewed the kh/ph/co2 relationship

240L tank:
Lights-on hours (co2 on)
kh- 2
ph- 5.9 i.e.co2 about 75.5 ppm

Lights-off hours (co2 off)
kh- 2
ph- 6.1 i.e. co2 47.6ppm (impossible)

160L tank:
lights-on hours (co2 on)
kh- 3
ph- 6.0 i.e. co2 90ppm

lights-off hours (co2 off)
kh- 3
ph- 6.1 i.e. co2 71.5ppm (impossible)

My fishes are all fine.

Since I cannot rely on the ph/kh measurement, I would like to compare notes with hobbyists experienced with this aspect, how many bubbles of co2 do you inject into a similar size tank to achieve 25 to 30 ppm of co2?

My own injection now:
240L tank : 3.2 bps
160L tank : 2.5 bps

Thx!!

[Plantbrain]

What are you using to test these measurements?

Small errors there can lead to large erros on the chart. I use a pH probe monitor and aLamott alkalinity test kits which makes for a pretty accurate measure. The presence of a non HCO3 buffer is unlikely if you do regular water changes, don't add peat/humics, don't add PO4 buffers to lower the pH.

I'd look elsewhere for the error if you preform the above water changes, don't add anything funny to your water. Otherwise blame the kits.

If the KH is really 1.5 that will drop the CO2 level by around 20ppm. One tenth of a unit off with the pH, drops the CO2 by 12ppm or so.

I give myself no less than 10ppm wiggle room. Which is fine for 20-30ppm range. You likely have a bit more than thius anyway. Tanks will buffer a certain pH also for a little while. If you let the tank go for awhile, the pH will rise more eventually.

Regards,
Tom Barr

[lip]

Thanks for your advice, Tom.

I use the JBL kh test kit, and pH pen (two pens now in fact, can't remember the brands). generally i get the same results on my pH pens. if there is a dif, it is only 0.1. So it doesn't account for impossible "high" co2.

I used to change 20% water every week, and for the past 2 to 3 weeks, I have changed about 40 to 50% water per week. I no longer add humic (black water)to the tank. the only stuff I add now are Seachem Equilibrium, Seachem flourish, and KNO3. I also add CO3 to my 240L tank to raise the kh by 1. I checked, and am told that it is only CO3, so should not skew the ratio. besides, it does not account for the readings for my 160L tank. P.S. will probably add a little of PO4 shortly.

Actually, i believe that I am not the only person with such problems. []

So it would be great if those with reliable results could share the co2 injection amount. I prefer not to just continue increasing until i see my fishes gasping at the top of the tanks (co2 then would probably be WELL above 30 ppm)

[PeterGwee]

Lip, are you using ADA aquasoil or Jobe sticks? ADA aquasoil is basically peat so as to speak and Jobe sticks leech lots of PO4 which will skew your KH reading as well. Basically, if you wanna get back the relationship, just do several large water changes as Singapore's tap contains less than 0.1ppm of PO4. []

Note: For aquasoil, I think it is gone case as it would take months or years to neutralize the peat effect.

[lip]

nope peter. i don't use any of those, though i do use root monster. if there is a leak and such leak affects the ph buffer, then it is probably gone case too because I can't remember where they are now.

[Allen_1971]

curious... did you cal both your PH pens recently... on the off chance that both are out of calibration.

[lip]

Hi allen, in fact, I was so skeptical about the results that i calibrate nearly every day... [:]

I have given up. will just monitor bba development and judge from there whether CO2 is enough.

I have also given up on the other test kits. Like what many others have experienced, these "affordable" test kits are only good for finding out whether something is present or not. Total waste of time if you want precise results. []

[Plantbrain]

Generally when I suspect something amiss w/CO2 I add more gas.
Most of the fish I keep are not troubled if I go up higher than the 20-30ppm. Some fish like Discus may get funny but most seem fine.
With two pens reading similar, it's likely they are doing a good job there.

Like PG's advice, give the tank a few good water changes to re set it and add the baking soda to get the KH to 3-4 range lower the pH to get around 30ppm with the gas and watch that plants.

I would not obsess much over it.
Regards,
Tom Barr

[lip]

Thanks Tom.

Yup, I have kind of come to the conclusion that I can't do very much about it, so why worry?

Let nature takes its course... []