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Are the feet sitting squarely on top of the joists? Say ~550L water (550kg), 100kg tank, 30kg gravel, 50kg stand + other, thats 730kg, loaded on 6 feet is over 100kg on each of those small points. Pretty risky IMHO, if the feet are directly over a joist its probably not so bad, but it would be a pretty lucky fluke if they all lined up!
Compromise is good but hard (I've been trying to figure out my compromise for my fishroom, changed my mind countless times this week!!), but you're going to have to do it. A festae might be a bit risky in that tank, I've been doing a lot of reading on them (trying to figure out a plan for all my fish, that bloody compromise thing again!) and I'm going to devote an entire 6x2.5x2' to my pair. You'll have a lot of bottom dwellers that in my experiences are pretty ignorant when it comes to respecting territories, and that is likely to piss off a big angry cichlid trying to defend his corner of the tank. Most CA cichlids have good teeth, the best example being P. dovii. click for pic