Hi,
For a few months now my betta fish has had a small white lump at the end of his tail fin. It's irregularly shaped and there are no signs of others.
It doesn't seem to have affected him too much but it may have gotten slightly bigger and we're worried about him. He's behaving more or less normally - maybe a little most sluggish than usual but hard to tell, he still swims around very happily.
He has been eating a lot of the algae wafers we have for the catfish we've got with him, and he gets bloated afterwards so we've been trying to keep him away from the catfish's food and feed the catfish peas, beans, etc which the betta fish does not eat.
1. Size of tank? 8L
2. Water parameters
a. Ammonia? (??)
b. Nitrite? 0
c. Nitrate? 0
d. pH, KH and GH? (??)
e. Test kit? Just a nitrate/nitrite test kit
3.
Temperature? 26 degrees
4. FW (fresh water) or BW (brackish)? FW
5. How long the aquarium has been set up? About 4 months
6. What fish do you have? How many are in your tank? How big are they? How long have you had them?
Betta fish - had for about 18 months, 1.5 inches
Bristlenose catfish - had about 3 months, about 1 inch long.
7. Were the fish placed under quarantine period (minus the first batch from the point wherein the tank is ready to accommodate the inhabitants)?
No they were not :(
8. a. Any live plants? Fake plants? Have had an assortment of various live plants, which kept on dying. Have had fake plants before but not now.
b. Sand, gravel, barebottom? Aquarium gravel
c. Rocks, woods, fancy decors? Any hollow decors? Have some rocks and a piece of mallee root.
9. a. Filtration? carbon/bioballs/sponge
b. Heater? 25W
10. a. Lighting schedule? What lights are used? THe light that's in the tank, they're LEDs, not quite sure the details. Usually turned off at night.
b. Any sunlight exposure? How long? Not very much, blinds are normally closed and window doesn't face much sun
11. a. Water change schedule? Once a week
b. Volume of water changed? 2L
c. Well water, tap water, RO water? Tap water, dechlorinated of course.
d. Water conditioner used? Don't remember the brand, but I can look it up if it matters.
e. Frequency of gravel/sand (if any) vacuumed? About once a week, but never thoroughly - we just fiddle around with it with the siphon.
12. Foods? Hikari betta pellets
How often are they fed? 2-3 pellets a day, down from 4 which we were feeding him the first year of life. Skip one or two days a week.
The bristlenose catfish is fed algae wafers about once a week, and peas every so often.
13. a. Any abnormal signs/symptoms? Just the lump
b. Appearance of poop? I saw him poop the other day and it was kind of a browny green - same colour as the algae wafers he likes stealing from the bristlenose.
c. Appearance of gills? Normal
14. a. Have you treated your fish ahead of diagnosis? Nope.
b. What meds were used?
15. Insert photos of fish in question and full tank shot if necessary
Here are the photos. It was hard to get one where the lump was easy to see. :(
http://i.imgur.com/mKUFW.jpg http://i.imgur.com/Erd6t.jpg 
