Well I had half wondered about that. It does kind of looks like a little white worm in a see through blister. There is some redness around the area. Even googling for worm pictures doesn't bring up anything that really looks like the things on my fish. I will try again to get a picture but I spent some time on it last night and that was the best of a bad lot.
Over the last 24 hours or so I've noticed 2 of my 9 cardinals have lumps on their sides. One on the flank and one just in front of the pec fin. They are perhaps not shoaling quite as well as they did but generally behaving normally. The tank has generally been healthy and harmonious. I'm still plagued by blue-green algae but it is manageable. Except for the pH creeping up over time the water quality has been stable. Readings from today have ammo 0, nitrite 0 and nitrate 5.
I can't find any pictures on line that really look like these lumps. They have a clear white edge and I wonder if they are bacterial ulcers?
I'm not sure the picture makes things any clearer!
OK, it seems the consensus is a blackout. I'll get on with the plan in the link in SO19's post. I'll keep the ferts going.
The link talks about low nitrate being a possible cause. I'm running around 20ppm. That seemed OK to me??
"As modern aquarists we know that algae is never caused by high Nitrates etc in a planted tank - More likely high Nitrates are caused by poor tank maintenance (if you're not dosing it with Nitrate) so easier to blame a number than inaction."
That's a fair point. This did all start when I was busy with other stuff and stopped looking after things and the water quality was terrible. Association is not causation after all!
Yes that description would fit. It did start at a time of very poor water quality although it is adequate now.
I'll try a few of your suggestions: I'll stop ferts and keep nitrate low (it is pretty much down to my tap water at present) I'll take another hour off my lights (3 on, 2 off, 4 on) I think the flow is pretty good but I'll stick an air pump in to improve flow and oxygenation. I'll give things a really good clean out (again)
"another factor there may be too much CO2"
Would you stop it? I'm desperately trying to get the grass to carpet and I'd also thought the CO2 would help the plants out compete. Having said that, I've got a dKH of 5 with pH of 7.6 and tap water (after 24h stand) of 8 dKH at pH 8. So my CO2 injection is doing virtually nothing. 2.3 to 3.7 mg/L according to the table I'm looking at. Maybe I need a better diffuser...
But I digress...
I'll try the above and leave the black out as plan b for now .