Betta eating less

Question
We got a beta for Christmas 2008.  We have been feeding it the beta pellets and it was eating regularly until recently.  We have two other betas in separate tanks and they seem fine.  The betas all eat the same food, water is changed at the same times, the same conditioners are used for all of them. Two of the betas live in the same room just in different tanks.  The one beta that is not eating very well is in the room with the other beta but not close enough to really know it is there.  We were using Aquarium salt in their water at one point but stopped when we noticed a film on the top of the two newer betas tanks.  The film has not gone away so we may try to put the aquarium salt back in their water.

But does anyone have any ideas as to why he is not eating as well as he was before, his tank is not one of the ones that has a film on the top of the water.  Does not appear to have spots that I can see and does not look bloated.  But I do not know what a constipated fish would look like.

Also any clue as to what is causing the film on the top of the other two beta's tanks.

Answer
Hi Paul,
If you look just where his chin is, a little lower, this is where his tummy is.  If this is swollen, then he is constipated.  If left untreated, it gets worse, the fish has trouble swimming, stays at the bottom or the top of the tank.  In the final stages it lead to Swim Bladder Disease.  This is due to poor diet, and overfeeding.  Try to feed him a frozen cooked pea.  Remove the outer layer, and cut into small pieces.  Try feeding the pea to your betta one piece at a time.  If he refuses to eat the pea, and has SBD, you will have to treat him with a good antibiotic such as Kanamycin.  Be very careful not to overdose.
It could also be that he is stressed.  Does he see the other Bettas?  Bettas should not see each other as they get stressed, and sick.
Feeding them Betta Pellets everyday is not good for them.  Their diet should be varied.  Betta pellets one day, betta flakes the next, daphnia the next, bloodworms the next, and one pea a week.   On the day that you give them the pea, they should have nothing else to eat.  This cleans out their system, and avoids SBD.  Always feed them small meals..example..2 pellets for one meal...2 flakes for one meal etc.  You may feed them small amounts 2 or 3 times a day making sure enough time as passed between each feeding.  Their tummy is the size of a betta's eye, and we must always remember this when feeding them.
When a Betta has SBD, do not add salt, otherwise you may.  If he is in a small tank, change all of his water, and clean everything in it.  Water changes should be made twice a week depending on the size of his tank, always with a good water conditioner such as Stress Coat, or AquaPlus.
Bettas should be in 5 gallons tanks or more.  They should have heated tanks.  They are tropical fish, and need 80 degree water.  In their habitat, the water may be shallow, but they have lots of room to swim.  When bringing up the temperature you must do this very very slowly.  One degree every two days as bringing up the temperature too fast would cause death.
The Betta is one of the most mistreated fish on the market, through no fault of the owner, but the vendor who will say anything to sell his gadgets to make a buck.  This turns my stomach over.  Bettas kept in small bowls, 1 gallon tanks, and vases will get sick, and are very hard to cure in such little water.   Betta living in bowls, or small tanks with no heater, and sometimes fluctuating water, is cold, and will get stressed, and sick.
This hurts the person who has grown so attached to his Betta.  They leave the store believing that they have everything they need, only to find out a few months later that their Betta is sick.  Money is spent to save him, and then more often than not, the Betta dies.
A well kept Betta should live 7-8 years when bought young.  Unfortunately we do not know their age when we buy them, which is why the Betta dies 3-4 years after we have them.  He is an intelligent little fish, and should be treated with kindness.  Unfortunately there are no laws to help the Betta, only information, which the vendors are careful not to give you.  Sometimes you do meet a fish manager who cares, but these are rare.  
For now watch the little fellow carefully, make sure that he wastes.  A betta who stops eating is never a good sign.  Examine him to see if his tail or fins are ragged, if his coat has changed colour, or if he has spots on him.
The white film comes from when they blow their nest.  They are actually blowing sperm.  I'm sorry I had to write this, but there is no other word I can use.
I have bred them, love them, so if you have anymore questions, please do not hesitate to write me.
I hope the little man gets well soon.
Lynda