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Old 09-23-2008, 11:49 AM   #40 (permalink)
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Default Re: CO2 system suggestions for a 75gl tank

Originally Posted by StevieD View Post
This has been a very informing thread. I just got a ph controlled co2 system. I love it. I use a drop checker with 4dkh solution to monitor co2. I really don't care what the ph is set too. This is a discus tank so i don't mind a low ph, but my water parameters are 6.08PH, 5GH and 4kH.

Earlier in this thread it was stated that phosphates can alter the reading of a ph monitor probe. It was also stated that it can effect the drop checker results. Can someone go into more detail on this? What levels of phosphate have dramatic effects on the ph controller's reading? If using a 4dkH solution in your drop checker, does phosphate have any impact?

This is a great thread for anyone with questions about co2... lots of unasked questions answered here!

Stevie D
Phosphates in your water do not affect the reading of your pH meter. The pH it gives you is correct for any buffer system. The issue is how the pH of your tank corresponds with the level of CO2 in your tank.

The whole thing comes from tables like this one:

If you go to this table, you will see that for your tank parameters at a pH of 6.08 you are well into the danger zone of CO2 level and it would seem that your fish are going to die. In fact this doesn’t happen because you have some other buffer system working in your tank (probably PO4). These other buffers interfere with the theoretical pH / kH / CO2 curve and give inaccurate readings.

When you use a bubble counter you fill it with a known 4.0 kH solution with no impurities. One part of the counter is in contact with the tank water and CO2 diffuses from the tank water and dissolves in the 4.0 kH solution. Because of the chemistry, after a while, the level of CO2 in the checker is the same as in your tank. Because there is no extra buffers in the drop checker, you can measure the CO2 using the pH of this solution. Typically this is done with a pH indicating dye. The color of the dye gives an indication of the pH and by inference the level of CO2.

Generally speaking what is in your tank water should not affect the drop checker unless some tank water contaminates the special solution in the drop checker.
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