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I wanted a tank that I could grow medium tech plants that required slightly more attention than low tech but without the co2 faff.. I use carbonated water for each of my 300mm cubes and have been doing so for about 2 months. I buy 2x 65p 2l bottles from the shop and does 6ml per day in each tank. good thing is its cheap.. bad thing is you have to replace the bottle when its about half way as the fizz goes! Its once again (as everything is) all down to personal results and preference.. In my case it works wonders, I base this on the size of my tank though.. My tanks are5 times smaller than yours so I would be unsure if it would have an impact, if any at all.. you could try liquid carbon as a substitute, but of course this does not match co2 quality.
Jack