Ideal kH for planted tank with fish?

kimmisc

kimmisc

is in your closet.
Mar 12, 2007
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Florence, SC
Just wondering what the ideal kH would be for a planted tank with fish and CO2 injection..

My tap kH is 2. I add baking soda to raise kH to around 5-6. With CO2, my pH is down to around 6.4-6.6. This is with Excel supplementation also, for now. (Excel lowers pH a bit.) This is during the day, so I assume it gets lower into the night. How high is too high when raising kH? Should I raise it more?
 
KH of 2 isn't bad but most will tell you 4-6 KH is the 'ideal' range. I wouldn't worry about your KH, TBH. If anything, add some crushed coral(good) or dolomite(better) to your filter instead of dosing baking soda.
 
Mine is 1 on a good day and I do not adjust it. My PH is 6 maybe less. The fish are just fine. PH changes caused by CO2 are nothing to worry about. Only real PH changes caused by KH changes are a concern. Besides some plant species will only grow well in soft water.
 
Don't get KH and GH confused. Water can have a higher KH and still be considered soft. KH is just the buffering capacity of the water and it can be depleted in time through plant photosynthesis and nitrification processes.
 
CO2 changing the pH should be a concern... if you have rock hard water and change the pH using CO2 you can easily suffocate fish, for example. Keeping things stable is key, which is why I think the dolomite or coral in the filter is a good suggestion if you are worried about KH. It will hold much more steady than dosing with Baking Soda (in most cases).
 
Too much CO2 is a concern but CO2 will change the pH regardless of how high or low your kH is, 30ppm of CO2 will drop your pH by about 1 in both low and high kH waters.

kH levels aren't really that important as long as your water has some buffering capacity (don't use distilled water). It's helpful in measuring how much CO2 is in the water but ONLY if there are no other buffers (like phosphate buffers) or acids is present.
 
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