I read something....somewhere...that paint fumes do indeed damage fish. So, turn off your airstone, (as Cear said,) but make sure water does not flow down the air tubing and into your air pump. If you have a large enough tank, (with my experience, 40 Gallons or larger,) water will come up through the air tubing and into the pump when the pump is off. This can be prevented with a check valve. These cost about a buck.
If your tank is smaller though, you may want to unplug your pump and test to see if water comes up through the tubing.