mfd is correct. I am a superman.
Anyhoo....
Chloramine is a combination of Chlorine and Ammonia. It is used in most municipal water treatment facilities, because it lasts longer in water than chlorine. This is bad for fish, not to mention for your body.
When you add a modern de-chlorinator product (as long as it says it detoxifies chloramines, it is modern) will break the bond and lock up the ammonia into a form that is not harmful to fish, but is still bio-available to the bacteria.
If you haven't cycled your tank, then you will continue to show high levels of ammonia in your tank until a biological colony forms that can consume it. When this happens, the consumption is almost instantaneous. This is why your tap water shows 0.25 ppm Ammonia, yet your tank shows no ammonia within a hour or so of your water change. With no cycle, you will still have the same amount of ammonia that is in your tap water.
After your tank is fully cycled, you can do PWCs without fear as long as you de-chlor the water - the bacteria will consume the locked-up ammonia very quickly.
In the meantime, I would treat your tank water daily with Prime and do PWCs. You can safely dose I think 3-5x the normal dosage of Prime directly into your tank to temporarily detoxify Ammonia, Nitrites, and Nitrates. The effect only lasts 24 hours. Check Seachem's website for info on that, you might have to search a little.
You do NOT need to buy an API tap water purifier for the reasons listed above. If you tank was cycled, you wouldn't have even noticed the issue, unless you tested RIGHT after doing a PWC.
A de-ionizer only filter will quickly burn out, causing you to have to replaced the media at great expense. This is why DI units are generally only used in saltwater applications, when you make your own RO water and want to polish it down to 0 ppm TDS before mixing in salt.
Otherwise, for freshwater applications, you would need to add in the beneficial minerals that you strip out. This in only really to be done as a last resort.
So take a deep breath, go get a bottle of Prime, and do a PWC at least every other day until you start to see the cycle.
See if you know someone who can take the fish in the meantime and use your tap water as your ammonia source!