Top it off: salt water or plain water?

Theres no water section so hopefully this will do. I have a simple question.
Should i top off my salt water tank with plain R.O. Water or salt water?
I hope to have a reef tank soon but for now i only have a polyp and a very angry anemone.

Fish:
1 Royal gramma
2 clownfish
1 blue spot puffer
1 mandarin goby

Other creatures:
4 snails
5 hermit crabs
3 sexy shrimp
2 pin cushion sea urchins
1 bubble tip anemone

Coral:
1 star polyp

All of which were very attached too.
Btw my tank is 65 gallons if i forgot to mention it