# high ph, hard water and co2?



## pyrrolin (Jan 11, 2012)

I finally decided to test my ph in my tank. I had just done a top up of about7 gallons in this 90 gallon tank so the reading could be .1 or so off but the reading I got was a ph of 8.2 which is fairly high but not a concern for most fish.

I will be adding pressurized co2 very shortly which will drop the ph during the day when it is on and here comes my question. If the tank is stable at 8.2 ph and the co2 drops the ph to below 7.0 switching the water from alkaline to acid, could this cause problems? The ph would climb back up again each night when the co2 is off.

I am not sure exactly how much the ph will drop with the co2 but would like to be prepared for any problems.

I will be using a drop checker with 4 dkh solution and I am using well water for the most part and occasionally getting a few gallons of water from a water softener system to help keep the iron from being too high. I have also added carbon to my filter which so far has been working well to keep the water from getting coloured from the iron. I don't like using carbon but need to in this case.


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## aniroc (Aug 23, 2012)

Changes in pH due to fluctuating CO2 levels are not dangerous to fish since there are no changes in osmotic pressure. Very high levels (over 50 ppm) can asphyxiate the fish by interfering with their own ability to eliminate CO2 in an already saturated water.
A drop of one unit of pH correspond to about 30 ppm CO2 if KH is 4 such in the drop checker.
How much your tank's pH will drop? It depends mainly on how high your tank water KH is (the higher the KH, the less will drop). However, there are other buffers (phosphates, borates, silicates, etc) and other sources of acidity (Fulvic acid, Humic acid, nitrification itself, etc), making the drop checker the most reliable way to monitor CO2 levels.


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## exv152 (Dec 1, 2012)

I don’t foresee any issues with adding CO2 to water with a pH of 8.2. Depending on what your KH is at, you’ll most likely want to drop pH by about 1 pH unit, maybe less (depeding on your drop checker and kh/ph chart). But I would not go with water from a softener because you’ll essentially be adding tons of sodium molecules. RO water is better because it actually strips the mineral content to reduce pH as opposed to binding minerals with sodium molecules, which is what a water softener does.


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## pyrrolin (Jan 11, 2012)

my fathers water softener uses potassium chloride not sodium so not adding salt.

I assume the kh is quite high in my tank, good to know that co2 won't drop the ph too much. I was just worried about the effects on bacteria going from acid to alkaline constantly if the ph dropped that much.


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## aniroc (Aug 23, 2012)

Healthy, fast growing plants will purify the water much better than bacteria. Excessive nitrifying bacteria is detrimental to good plant growth.
Also, ammonia (ammonium) is not toxic to fish if pH is less than 7.


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## Sameer (Sep 30, 2007)

My ph is 7.8ish in the mornings and Ive set my ph co2 controller to 6.4. It takes around 20 min to hit that ph. Fish are not bothered. In the past, it used to go down to 5.9 to 5.8, which is the extreme end. My fish were stressed and gasping for air. So Ive never gone close to 6 again, its overkill as well. So drops by 1 are not a problem, I think you wont go that extreme and if you acclimate your fish to drops like that, its not a problem.

As long as the drop checker is at the colour its suppose to, its fine. The checker isnt the best thing but its the closest thing we have. It is delayed though. As long as you are not hitting dark yellow to orange, you are fine. Usually its said that the best indicator is your fish. It will take weeks and fine tuning to get it right.


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