My question is if we are only changing 10% of water with water that is higher or lower in alk will it actually make much of a difference in the tanks total alk? Would be an interesting experiment. How much will a 10% change with say 11 alk water actually change the tanks alk after the change? sounds like a good test in the future. In the past I have never bothered matching my alk unless I am doing a massive water change. with a normal 10% change I just mix it up and go with it.
Jeff
It just changes 10% of the difference in alk.
So if tank is @ 8 dkh, and new mix is @ 11 dkh, and a 10% water change is done, total alk change in tank = 10% x (11-8) or 0.1 x 3 which is 0.3
In this example, our tank goes from 8 alk to 8.3 alk. No concern for me.
I actually do this every week, as my tank runs close to 8 and I use reef crystals. My dosing is simply adjusted accordingly to maintain weekly stability (the 8.3 will be back to 8 by next water change).