Since when is 7.4 the magic pH number? All but the most sensitive fish can adapt to a wide range of pH's and it's best to acclimate the fish to your tap water than to futz with it to make it lower. My pH is 8.0 out of the tap with a GH of like 4 or 5. I've kept bettas, honey gouramis, several kinds of tetras, german blue rams, otos, gobies, nannacara, guppies, sparkling gouramis, chocolate gouramis, scarlet badis, and a ctenopoma acutirostre.I would suggest testing your tap water first of all, check the ph and ammonia in the water. Always use a dechlorinator, I use prime as its concentrated and very cost effective. If your ph is high in the tap water then use RO to keep the ph around 7.4
The key to keeping most fish is not to have an ideal pH, but that whever the pH is, it stays stable and consistent.