I have very high current flow (which breaks the surface) and use additional aeration. My plants are continuously pearling which indicates O2 saturation.
How do you measure 50-80 ppm CO2? Also, what is your tank kH and do you have any other alkaline substances like PO4 in your water?
Why don't my fish die then?
Even large full adult wild discus, they breed at 45ppm.
Pearling is NOT a function of O2 saturation.
I have very pure tap water. They do not add any phosphates and there is no non carbonate alkalinity.
CO2 is measured via silicone porous membrane if a small reference cell of about 200ul using a special flat tip probe. This flat tip reduces the lag time to under 2-3 minutes. A rubber grommet seals the reference cell and only dissolved gas can move across the membrane.
I also have an Oxyguard meter. It's fairly accurate in general.....but lag time and referencing it with their protocols is questionable, I simply just did the below:
A reference measure is taken by using a batch of RO/DI water and then made to a KH of 71.44ppm alkalinity using sodium bicarbonate. This has CO2 added via a needle wheel until I get a stable reading of 50ppm using the KH/pH relationship. This is done in a bare 10 Gal tank with about 20 liters of water.
This gets me to within about 1ppm of accuracy.
The CO2 reference cell flat tip works very well, takes 2-3 minutes to settle and then it's relatively easy. I have to add fresh solution and membranes about once a month as long as it's kept wet and in the dark.
Since the tap is also pure and I do add some PO4 as KH2PO4, but this is not alkaline......I might add a few ppm to change the KH maybe 1/2 a degree at most.
This is still a long long way off from your 33ppm. No matter how you cook this turkey, there's something else going on there. I've been keeping 30ppm or more CO2 levels since 1996. If anything..........a method to measure CO2 will always OVER estimate the true concentration as CO2 [aq], it will virtually never UNDER estimate.
Unless your pH meter is really whacked etc maybe....... There are plenty of examples of folks going back to the mid 1990's where 40-100ppm where used without issues.
I came up with a max for adult wild discus of 45ppm, they where the most sensitive of the fish species I've used/had. They turned dark and behavioral changes at that level, it was a non lethal level in other words.
A simple RO/DI water and a basically makign a good size KH reference solution, then using a freshly calibrated pH probe should suffice for adjustments to the reference CO2 method chosen. This can be done is a 5 Gal bucket etc, a scale to weight the sodium carbonate of baking soda etc.
Even if there's a little water hydroscopic residual...in 5 gal you will still be pretty darn close.
Some folks compare their tank water pH at ambient to the reference KH solution pH in a sample that's had plenty of time to degas.
Then they make an adjustment based on that difference.
Say the pH is 0.3pH units different, so instead of a 50ppm target and a pH of 6.2, they add enough to push it to 5.9.
Their 50ppm target without this correction might mean 20ppm of CO2.
This tank is 60ppm:
Not many fish, but plenty of shrimp's, gold nuggets are particularly sensitive to higher CO2, there are 3 in here.
This tank consistently has 70ppm.
Plenty of fish, but most in the pic are not that sensitive to CO2 levels at the higher ranges.
in general, PO4's do not influence pH/KH measure a huge deal, but might move them perhaps 5-10ppm.
Not 200-300% different.