Hi Cheryl & welcome to Planet Catfish
Initially the tank wasn't mature enough for the fish as ammonia & nitrite should be zero. It sounds like you have started on the right actions with combating the water problems - further small & frequent changes combined with upping the aeration should help.
Your syno (Euptera) has quite a deformed face as it is extremely blunt & may be the sign of a poor quality fish. Also this species is very adaptable but the tank set-up seems less than perfect as coral & ocean rock 'produce' hard alkaline water suitable for rift synos whereas this fish is a riverine species. It should adapt to this set-up though.
There are a couple of "types" of synos going white. Your fish looks to have rubbed it's body on rough decor or sand, perhaps combined with irritation of initial poor water - if this is the case it should recover in time.
The other sort tends to start with a whitening of the lateral line then lead to bold white body blotches which seem irreversible. The cause of this is not fully confirmed