Many fish can adjust to different ph's as long as the ph is constant. It's when the ph crashes that there's issues. If you'd like to raise the ph, crush coral will do it, but with a constant drip, I'm not sure what the effects would be.
Personally, I'd say you're fine. The less you mess with the water out of the tap, the better. If you're on city water, you're going to need a chlorine filter (charcoal) and a chloramine filter if there's chloramine in the water. You'll most likely need to call your water supply company and find out what they use. Filterguys.com sells a chlorine/chloramine filter for about $80. For mine, I just used an RO filter with all charcoal filters to get rid of the chlorine as there wasn't any chloramine in the water tests.
Also, sorry to be a debbie downer, but you're going to need a tank about 10-12x the size of the tank you have now to hold all of those fish. Healthy TSN's and RTC's will grow to 3-4 feet easily within the proper conditions...and grow quickly. I'm not sure the size on the gator gar, but I'm sure it gets bigger than bot the cats. Perhaps you know this and already have a pond built for your big fish, so I'll leave it at that.