Kerrie

I wouldn't worry about the alkalinity. I am sure the fish being sold in shops are in plain Wgtn water. You could ask them to test the pH of their shop tanks to check.
The acidity is more important when breeding them.
Once you start mucking about with the water you have endless problems keeping it stable, especially in such a small tank.
I used to keep Africans and they were perfectly happy in neutral water instead of the alkaline waters it is said they prefer. The breeder pointed out he was breeding them in neutral water and since his fish couldn't read they didn't know they were supposed to prefer it a lot more alkaline 
How alkaline is Wgtn water? It surely can't be too bad as councils try to keep the water as neutral as possible to protect the pipework.

As Caryl has said it should be good to go using tap water.