Is it ok for me to do this?

thanks alot steve

 

yeah just use straight tap water, dechlorinated if you can.

you'll have a large diatom bloom but nbd. this is how i started my tank

 

Not to sound like a jerk or discourage you but if you cannot afford RO/DI water to start out right you may be in the wrong hobby. Water is the single largest ingredient in your reef tank and everything depends on it. My thoughts are start it out right from day one and provide the best you possibly can. I am a water treatment plant supervisor by profession and I won't use tap in my tanks.
Don't skimp on the water, many things in tap water are cumulative meaning they will never be removed no matter how many water changes you do with RO/DI. Once its in the system, sand and rocks it does not go away. Why chance it?

 

It's not that the tap water would eventually be filtered out. The problem is some of the bad junk in tap water will be absorbed by your rocks and will eventually leach back out into your system. I say go RO the whole way. I'm not 100% sure on the exchange rate but £36 (my guess is around $55-$65?) for a tank full of RO and therefore peace of mind sounds like a small price to pay. Many of the fish you'll be buying down the road will be in that price range anyway. I say bite the bullet. But that's just me. It's an expensive hobby, ya know?

Dechlorinated if you CAN?! Dechlorinating is NOT an option.