Unfortunately it's hard to help without knowing what your water is doing.
Is there any way you can get a pic of the raised area? It could be one of a number of things so a picture would help identify it.
But first things first - water quality. Unfortunately you have way too many fish in that tank so to keep the water healthy, you should really be doing about 60%+ waterchanges twice weekly especially if you have commons in there. Is 11 the total after 2 died? (which i'm sorry about

). If so, you have 10 commons (10 x 20 gallons) plus one blackmoor (1 x 10 gallons) in a 55 when for the sake of their health, they should be in 210 gallons... Also, it would help if you can look at investing in more filtation. The 2 you have currently turn over 460 gallons and you want to try and aim for 10 x the filtration (550 gallons per hour) or more for your stocking situation.

So if you can, please try and post back some water parameters and a pic and we can take it from there

PS. I just wanted to add, commons and fancies shouldn't be together. Commons are much faster and more territorial so try and keep an eye on your moor.