I agree with the others, you are in for trouble down the line. Everything you have needs moved to a bigger tank. A normal 55g would be too small but a hex just makes matters even worse.
You are looking at a minimum of a 5x2x2 to house that lot as adults, 4x2x2 if your plecos are bristlenose and your eartheaters are not potential 12" fish. You will probably be down 2 clown loaches as the oscar grows, their growth rate is incredibly slow and the oscar will simply out pace them.
Going by your stock I would guess you were advised by your lfs that these would be ok and the usual plecos they offload on unsupecting customers are common plecos or sailfin plecos. Either way your looking at atleast 18" for your pleco if it is one of the two commonly sold ones.
For future reference, foot print is what matters on tanks that house larger fish. All these fancy tanks, hex and cylinder, are only really good for dwarf cichlids and other fish under 5". Unless it is a huge custom built hex or cylinder of course.
Edit: Just read your post above mine, please get a name for the pleco and or a pic so people here can ID it for you unless you have a firm ID already. I have seen commons sold with the info of up to 8" or sailfin plecos that get to 10" max.
With no oscar, small eartheaters and if your pleco is one of the smaller kinds then a standard 55g will leave you with room to get a few more fish. But bigger is always better

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