What is the
TDS of your tap water? Phosphates? Nitrates? If you have low
TDS and 0 Phosphates and Nitrates then you're going to be in much better shape using tap water than someone else. Because tap water varies so greatly from area to area, city v. well it is really hard to say what
your tap water is going to present to your tank in the way of challenges.
We started our tank (in October) with tap and have just recently switched the water over to
RO/
DI. Really for no other reason than that we
should be using
RO/
DI water, the tank is in perfect shape with no algae to speak of. The unit we got was from eBay. It is from FilterDirect and ran us around 90$ for 100g a day (which, I have to tell you, looks incredibly slow when you're watching it pour)!
Certainly
RO/
DI is the way to go if you can and in this hobby the 100$ is well worth the peace of mind that nothing that I'm not intentionally putting into my tank is getting into my tank.