White bump on Cory's dorsal

[Kets]

1. Water parameters
a) Temerature range.~75 deg.
b) pH. 7.2
c) GH. ?
d) KH ?
e)Ammonia, Nitrate, Nitrite, leavels. 0/0/20
f) Water change frequency 25% per week
(Most LFS's will check your water and give a list of readings).

2. Tank set up
a) Size. 20L(Long, not liters btw)
b) Substrate. Shultz Aquatic Soil
c) Filtration. 110 GPH
d) Furnishings. Valisneria spiralis, Hygrophila corymbrosa stricta, H. Polysperma
e) Other tank mates. Mollies, Guppies, other cories
f) How long has it been set-up? Months, but recently moved the cory from a different tank (20H, Same parameters, tankmates were swordtails instead of mollies/guppies, same water change frequency, Valisneria spiralis, V. americana, V. a. gigantea V. nana, a rock for furnishings)

3. Symptoms / Problem description
There is a white bump on his dorsal fin.

[Coryman]

Do you have a picture of the fish? It could be a parasite cyst or even just a fatty growth, which are usually caused by high protein food.

Ian