Depends on what you mean by high.. 7.0-8.0 I wouldn't touch it. 8.0-8.6 is okay but you could consider cutting it with RO, imho, especially if it's much above 8. Above that I would cut it 50/50 with RO. If it's 9+ it really needs to be cut. It's not hard, but it's a little tedious and very important to do it precisely and exactly the same each time with exact same water sources, and I would be owning gh, kh and ph test kits.
Last edited by callistra; 01-21-2013 at 03:21 PM.