If you've been doing a lot of water changes and are still getting a .5 reading you may want to check your tap water. Many water companies use chloramine in the water which will give you an ammonia reading. As long as you are using a dechlorinater it is safe for your fish. If you cut back on water changes to once a week the bacteria should be able to get the ammonia in your tap water.
If, however, you have not been doing a lot of water changes then you should do a large water change and clean your substrate really good to make sure it isn't old food and poop making you ammonia level go up.
Another thing would be to ask your water supplier if they are adding ammonia or ammonium(harmless). Some test kits will also detect ammonium levels which will show on your ammonia test result.
They are the same thing! Ammonia is NH3 with no charge. Ammonium is NH4 with a +1 charge. But they freely convert to one another all the time.
NH3 + H+ <--> NH4+. The ratio of one to another is mostly determined by pH and a little bit by what else is in the water.
I've written up more details here: http/www.fishforums.net/index.php?/topic/154313-of-toxic-ammonia-charts/
Also, the above link helps answer the OP's question.
I am more concerned that a fully cycled tank doesn't seem to be able to handle 0.50 ppm of ammonia quickly. If the tank is fully cycled, even with 0.50 ppm ammonia in the tap water, the bacteria should handle that in just a few hours.
Though I also agree to contact your water company. 0.50 ppm is rather high to be drinking from.
Many of the common aquarium fish can adopt and live very happy healthy lives in that water. Heck, most of the Rift Lake Cichlids would love that water -- the African Rift Lakes are very basic.
Unless you are specifically trying to breed or keep wild-caught or other delicate species (this is where research becomes necessary), a stable pH in the high 8s is fine for the vast majority of fish available at any LFS.
Trying to tinker with pH could do more harm than good if you add chemicals to the water.
Okay cheers for that info,i wont reduce ph, im currently treating my tank for finrot, and trying to get to the root of the problem,i checked my ammonia levels today to,and they were 0.25,have you any suggestions as to why the bacteria in my tank isnt getting rid of the ammonia thats going into my tank from my tap water,any help gratfully recieved,i also clean tank every week with 40% water change and gravel vacuming