Iron and pH
Good morning molly...
I've never heard of a fertilizer changing the acidity or alkalinity of tap water. Trying to change the pH of your tank water isn't recommended, because it's difficult to maintain a specific level. Unless you're keeping rare fish species, pH, hardness, etc. really aren't important for keeping a successful aquarium.
If you just treat your city water for chlorine, chloramine and ammonia, your fish and plants will adapt to the water conditions. They've been doing this for a long time.
B