Well, I am afraid you will not get much help from members if you are not willing to give us the data necessary in order to answer the question. And it is not very responsible to not know what is coming out of your tap. Fish live in water and its properties substantially affect their physiological processes. This is a scientific hobby, plain and simple, and it doesn't take much effort to fathom the basics. And this is the only certainty to good fish health.
You could put a bag of peat in the filter and if your GH and KH are very high, it would have next to no effect. But in a low GH/KH the effect could be considerable. Then there is the rate at which this becomes exhausted and has to be replaced, again determined by your initial GH/KH.
You don't need test kits for this. The GH and KH of tap water is unlikely to alter, and you can easily ascertain it from the water supply people, usually on their website. This is basic fiskeeping 101. Once you start fiddling with water chemistry as you intend, you can cause a lot of problems if you don't know what you're doing.