Acceptable PH variation for a discus and achiving stable PH/KH?

[Beurre blanc]

Hello guys. I'm wondering what is a acceptable ph variation for a discus. The reason why i am asking is that my KH is a little bit low and therefor it dosn't buffer well enough. When i do my 40-60% water changes the ph will normaly go up to a 6,9 at maximum. My Co2 system will then kick in and start producing as it's set on auto-ph with a KH of 3 which means the best ph is 6.6 (also where i want it). The ph will then drop in 2-3 hours down to about 6,56 in ph, making the co2 production stop and the ph change get slower. Over the next 10-14 hours the ph will drop lower, down to 6,33 which is the lowest iv'e seen it. At 6.33 the ph stabilizes and stays there to my next water change, going up again to 6.9 when i'm done.

What i'm hoping to achive here is to find a way where i can have my ph stable at about 6,6-6,7 or as close as possible. That way the co2 system can regulate itself when it's enough co2 instead of the system stopping becaouse the ph is to low. The cheapset and so far best way to raise my KH has been to use baking soda. However what i'm wondering is it any of you guys that have any better suggestions? Also since this is a planted tank with discus i want to keep ph changes at a minimum. The changes i'm explaining here will it cause stress to the fish, or is it small enough to them not being bothered? Thanks for any help :)

Fredrik

[plecocicho]

Your fluctuations are nothing to worry about, rule of thumb is less than 0,5 ph change per hour.

[Poco]

Have you tried ageing the water in a barrel with a heater and air. just age it for 24hrs and this will eliminate your pH swing. Any pH swing will add to stress levels, if you can avoid it then why not.

[Beurre blanc]

Super, thanks for the tips guys. :) I'd love to age the water but i simply do not have the space to do it. :( It was hard enough to fight thrue having the QT tank operative inbetween the baby wagon and the rest of it. :)

[jimg]

It's not a bad drop but I would keep it closer. the best way would be to do smaller wc's with aged water. you can use baking soda but I prefer crushed coral, a small amount in a stocking or mesh bag under the filter exhaust flow works fine. .