Kurt_Nelson
Aquarium Advice Addict
Yes, I keep a close eye on salinity. 5g evap over a week out of 75g doesn't change the salinity that much (especially with all the ... salt creep that I seem to have),...
Actually... it does. If you start with 75g at 1.023 and let 5g evaporate without topping off, you end up with 70g at around 1.025. Over the course of a week, that's a fairly gradual shift and probably isn't a big deal to the fish.
... and replacement water is introduced with a air tube siphon and 5 gallons takes about 30 minutes to drain in, so even the replacement happens gradually to avoid massive swings.
30 minutes to go from 1.025 back down to 1.023 isn't really gradual. Granted, those types of swings might happen over say 60 minutes when you're acclimating a fish that you just brought home from the LFS, but that's a one time thing. Doing it at every water change is a little different.
Since you say you don't have corals, then it's probably not that big of a deal. But if you go down that road, don't expect them to take to kindly to those types of swings.
Regarding alkalinity, I'd consider anything between 8 and 12 dkH to be just fine. You keep saying your alkalinity is "so high", but I think it's right where you want it. I think your LFS is feeding you a little bad info - buffers will temporarily increase your pH, but it's just a quick fix. The main point of buffers is to increase the alkalinity. Here's a good link to understanding some of the many reasons your pH can be low...
Chemistry and the Aquarium