It's been too long since I've done it. I don't remember. I would do trial and error...add a bit and test pH, etc. 1 tablespoon sounds like a good starting point for that size tank.
ok
ive chucked in a bit of that, will test it when its gets upto temp etc, if i need to lower ph do i just add vinegar or something?
also the guy was out of stock of 200w heaters so sent me a 3oow, thats ok isn't it?