Remove that carbon, you really don't need it unless you're trying to remove meds or something. Gravel is a really messy substrate. I gravel vac my substrate every time I do a water change and even if it's only been a few days since the last one I am always pulling a LOT of crap and leftovers out of it (and my tank is about the same size with 1/3 the bioload.) I would reccomend you get a gravel vac and keep the hidden mess in the substrate under control. When was the last time your filters were cleaned? That may help a little if it has been a while.
EDIT: I just noticed your stock list, and IMO a tank that size with that many fish (especially of the CA/SA cichlid variety, most of which tend to get some size on them,) is quite overstocked. I realize that most of your fish are juveniles right now, but fully grown a similarly sized tank would only be suitable for 1-2 jack dempsey/green terror sized cichlids if you want to keep everyone as happy as possible while keeping everything nice and clean. And I mean no offense by this, but why are you considering adding a dovii? Minumum tank size for a grown dovii is over twice the size of that one, not to mention it will already be really overstocked as your other stock grows. This is probably why your water isn't as clear as you want it to be.
EDIT: I just noticed your stock list, and IMO a tank that size with that many fish (especially of the CA/SA cichlid variety, most of which tend to get some size on them,) is quite overstocked. I realize that most of your fish are juveniles right now, but fully grown a similarly sized tank would only be suitable for 1-2 jack dempsey/green terror sized cichlids if you want to keep everyone as happy as possible while keeping everything nice and clean. And I mean no offense by this, but why are you considering adding a dovii? Minumum tank size for a grown dovii is over twice the size of that one, not to mention it will already be really overstocked as your other stock grows. This is probably why your water isn't as clear as you want it to be.