Help! Test Kit Discrepancy

[catwoman]

I have been using the Nutrafin KH test kit for the last couple of months to monitor CO2 levels and to determine how much baking soda to add. I just got a Aquarium Pharm test kit for KH and decided to compare the results. Nutrafin gives me 90ppm KH and Aq Pharm gives me 143.2ppm That's huge. Anyone else have these kits or have had this problem? Which one do I believe?

 

[Scougie]

They both seem way high. If your KH is really 140 something your fish are probably floating on the surface unable to breath! You need to know your PH and your KH to work out the CO2 content of the water this link will help it does the maths for you! Measuring CO2 levels

 

[Bangin]

I think Scougie has ppm confused with °kh. According to those test results you're somewhere between 5-8° kh. What is your pH reading?

 

[Scougie]

Err yes well spotted Bangin!! )

 

[catwoman]

yes, my readings are in ppm. My Ph is 6.9. I use Chuck's CO2 calculator which means my CO2 is around 40ppm if I believe the AP test. My tap water resting Ph is around 7.4. When I test the tap water KH, I get 10ppm from the Nutrafin test (1 drop) and 35ppm from the AP test (2 drops). I have been adding baking soda to get to 80ppm based on the Nutrafin test for the past few months. I've had trouble getting my Ph down below 6.9 with pressurized CO2. Maybe that's because my KH is way wrong. I think I should be believing the AP kit.