fin rot? + diet question

Question
QUESTION: Hi Lynda,
how are you?  I think my girl has the beginnings of fin rot, and that is because suddenly there is a darkish ring around her tail at the very edge.  I've read that fin rot is caused by bad water, but I had just changed it the day before, and I do 100% water changes every week in an uncycled 5 gal. tank with good conditioner and salt...What do you think could've caused this?  
Also, I wanted to ask you, what do you feed your bettas?  and when?

ANSWER: Hello,
Bettas should be kept in heated water.  They are tropical fish, and need 80-82 degree water to be comfortable, and stress free.  If your betta is in cool water, he is cold, and this could be a reason.  They should have a thermostat, and never be heated with lamps.  When heating water for a fish, you must do this very very slowly.  Bring the temperature up one degree every two days, as bringing up the temperature too quickly would be deadly.
For now I would wash everything in his tank with warm water, the gravel, and the ornaments.  Do not use anything else but warm water, and clean it very well.  Add 2 teaspoons of diluted aquarium salt for one week, and when changing his water again, add one teaspoon.
If his condition worsens, write back to me.
Here is a list of foods that bettas should have:

Betta Pellets
Betta Flakes
Daphnia...Daphnia is very important because it helps their digestive system
Bloodworms once a week as a treat
Mealworms
Glassworms
Brine Shrimp
Plankton Flakes
One pea a week, and on the day you feed him the pea, feed him nothing else.  This is so he can clean out his system, and avoid SBD.
Bettas should be fed 2-3 times a day in small amounts.  We must always remember that their tummy is the size of their eye when feeding them.  Two pellets, or two flakes is enough for one meal.
I hope  this helps.
Lynda

---------- FOLLOW-UP ----------

QUESTION: Hi , Thanks for the diet tips!
Ok, so, her water is 81degrees, I bought a heater, but it took me a long time to trust it, so I had to keep plugging and unplugging it to raise the temp. slowly...the problem I fund after that was, once I got it to the perfect temp., I had to unplug it every night to make sure it didn't raise up over night! But then, in the morning, It had dropped a couple degrees!!  REAL bummer, and I'd have to start over, raising it slowly... It doesn't have its own thermostat, I just use a thermometer. Now, I finally got it to where I can leave it on all night and it stays at 81.
When you say wash everything in warm water, should I also wipe down the sides of the tank, and sort of scrub the gravel and toys with my hands? I have only been rinsing everything without wiping the natural "scum"or mucous she produces and lines the tank with naturally, thinking she might need that to make her feel at home...
THANKSSS!

Answer
Hello,
Yes, wash everything. Remove the gravel, and wash it well.  I use a small pail, and swish the gravel around until the water is clear.  Keep rinsing.  Remove the scum with paper towels until there is no more left on the walls of the tank.
Fluctuating water is very bad for fish, it can really harm them, even kill them.  This is the reason she got sick.  Hopefully now with the water change, and temperature remaining stable the little lady will improve.
Lynda