Salt to the tank. 1tsp per gallon and be careful of any salt sensitive tmates. Could try API fungus cure as it works well or MB dip. What's ur water parameters? Tankmates? Heater covered? Better side shots of the senegalus please.
Unfortunately I'm about to head to a funeral so I used an api test strip, I'll do a liquid test when I get home. I did just add 5 tbsps of salt. It's a 30 gal, or 29 high. There's a little bristle nose in there. Looks like 180gh. 80kh. 7.5ph. 0 nitrites 0 nitrates. 78/80 degress F. Lfs opens in 3 hrs so I'll go get some fungus cure. Tossed in a lil stress coat as well.
Heater not covered, I was thinkin about that as well. My elodea plants are looking rough in that tank as well, pardon the mess, I'm doin a water change and rearranging tanks later today. See how brown they all are in the 30gal (lots of plants) as opposed to my 10gal guppy tank? I thought it may be light but seeing my poly now makes me wonder what else is going on.
Better photos would help. From the straight on it looks like fungus. Side shots will help to tell cause the pleco can do the same. Especially if not fed and all the areas are circular and about the same size.
Heater burns can take of the slime coat and fungus will grow there as well. Something to keep an eye out. Pics will help to clarify.
I'm not the best at diagnostics, but it looks like some sort of growth or fungus. Would highly recommend posting in the diseases section as
Hendre suggested. It would also be helpful if you post your water parameters ( ph, ammonia, nitrites, nitrates, and temp). Really hope your poly gets better.