10 is going to be rather high for most fish and will likely kill your plants as well. If that realy is how high it is (are using test strips? They're inaccurate - use a liquid-based kit instead), you should look into getting an RO unit or filtering your water through peat or something. BTW, are you testing your actual tap water or your tank water? If it's the tank water, make sure you don't have any rocks or ornements in there that could be contributing to the hardness and buffering the pH - things like crushed coral and limestone do this. Normaly I'd say not to alter your pH but you probably will need to unless you go for a species that does well in such alkaline water. TBH though, not even the rift lake cichlids of tanganyika live in water with a pH much higher than 9.1 or so. Maybe they can handle higher but I've never seen any kept in such conditions.
