I was told by a person that you can simply fill a soda stream bottle up with tank water and do the squirt thing into it and put it back into your tank.

not sure if your saposed to just pour the whole bottle back in straight away or what? have read about ph increases etc etc.

any one know? is it safe?

Not quite. I used to use the soda stream bottles about 10 years ago when they were a heck of a lot cheaper. I got a regulator that fitted the bottle and fed the gas to a diffuser inside the tank. Very cost effective and handy - I could swap bottles at local supermarket during my grocery shopping!

was told by a person that you can simply fill a soda stream bottle up with tank water and do the squirt thing into it and put it back into your tank.

So you want to add soda to your tank? Sure you can do it.

Whether or not your fish survive is another question.

pH will crash drastically and you'll kill your fish. Carbonic acid and all.

like i said i was told by somebody thats what they did, i thought it sounded strange..