Definitely check your Nitrates.
When the water comes out of your tap, if normally contains CO2
. Once the CO2
has offgassed, it will raise the pH to it's normal value. Best way to check this is to let a cup full of tap water sit out for a day or two then measure the pH again. By that time, the CO2
and other gases will be offgassed and give you the correct reading.
A pH of 7.4 is no way alkaline (ok it is, by definition, alkaline). It may be a little higher then neutral, but no where near unacceptable. The pH is driven by the buffering capacity of your tank. IE KH
. Having a pH of 7.4 is a good thing. I, personally, would not change it. All you are adding is probably a phosphate additive that is NOT needed.
Most people, if not all, would recommend not touching your pH unless it is WAY outside of the norm. Something like 8.8 or 5.4.
It is BETTER to have a constant pH, rather then have one that is buffered and changing. You want STEADY parameters.
As far as size goes, 5" isn't that big, but you have to understand that a fish will NOT grow to the size of the tank, no matter what the LFS
or friends have told you. The inerts of the fish will be crammed together and make the fish very unheathly. That is something you will not be able to see on the outside. Having those fish at that size, I doubt it is internal at this point. Clean water is your best defense rightnow. Slowly increasing your PWC
's to about 50% per week. I, personnaly, would stop changing the pH.