Okay...your tank is EXTREMELY overstocked...Even if they are young fish now, there's still too many for a 55 gallon. The fact that they will mostly outgrow this tank very quickly doesn't even matter at this point. I popped your fish into aqadvisor.com with your filters just to see what it said and here's the result:
http://aqadvisor.com/AquStockImage....200912081400:,1:200911111527:,1:200909300234:
That's NOT including the pleco, since I have no idea what type of pleco and they come in a wide range of sizes. So, while aqadvisor is just a helping hand, and I don't think it's necessary to abide by its suggestions completely, it clearly states that you are seriously overstocked.
In fact, the actual site (not the generated pic) says:
"Your tank is seriously overstocked. Unless this setup is temporary, you should consider a larger tank." WithOUT the pleco.
It also states many issues with the fish being housed together:
"Warning: When Convict starts to breed, they may become too aggressive to co-exist with Apistogramma Parrot.
Warning: At least 5 x Silver Dollar are recommended in a group.
Warning: Jaguar Cichlid is not recommended for your tank - it may eventually outgrow your tank space, potentially reaching up to 14 inches.
Warning: Apistogramma Parrot may become food for Jaguar Cichlid.
Warning: Flowerhorn is not recommended for your tank - it may eventually outgrow your tank space, potentially reaching up to 12 inches.
Warning: Apistogramma Parrot may become food for Flowerhorn.
Warning: Your selected species may eventually require 562% of your aquarium space. You may need to deal with territorial aggressions later on. Try removing some of (Apistogramma sp. Parrot, Cryptoheros nigrofasciatus, Rocio octofasciatum, Herichthys cyanoguttatus, Parachromis managuensis, Aequidens pulcher, Flowerhorn, Cichlasoma Salvini) or get a larger tank.
Warning: Water temperature requirements are not fully compatible between all selected species.
=> 24 - 29C: Apistogramma Parrot
=> 20 - 26C: Convict
=> 22 - 30C: Jack Dempsey
=> 24 - 28C: Silver Dollar
=> 22 - 30C: Texas Cichlid
=> 25 - 28C: Jaguar Cichlid
=> 18 - 28C: Blue Acara
=> 27 - 32C: Flowerhorn
=> 22 - 27C: Tricolor Cichlid
You might want to consider getting a second 55, or even a larger tank and splitting the stock up into better grouping. Also, most species of pleco get too large for a 55g so I hope you have a dwarf species.
This fish load is probably one of the main issues you're having with cycling your tank and keeping parameters safe. =/