Betta Fin/Water Problem

Question
Dear Chris,
I apologize in advance for the long explanation here.
I have been bitten by the Betta Bug since I bought my first one over 2 months ago. I now have 4! However all of them but the third one, weather kept separate or together(in split tanks of course), seem to develop red streaks in their bottom fin and tail. I thought this was fin rot.
The first one I had would not eat until I bought him freezdried blood worms so that is what all of my fish eat. I kept him in a 1/2 gallon tank with no filter, I treated him for fin rot with the yellow powder inside pills made by Aquarium Pharmaceuticals, and it went away and his fins were growing back.
I bought a second one and kept them both a week or so in separate containers before putting them both in a split tank of a combined 2.5 gallons with a mini aqua-clear filter set on LOW(I was told this was an appropriate filter, and that some kind of filter was good for them and would make a difference in their fin appearance over extended periods of time?)I figured it would help keep their water cleaner and make them happier and lower maintenance. They have silk plants for decoration, small statues and seaglass on the floor of the tank. Neither showed red streaks before I put them both in brand new water neither of them had been in before. My second fish then developed the same red streaks and the firsts fins started to deteriate, no red streaks. So I went to a very reputable pet store and they recommended Jungle Fungus Eliminator. I have been using that in the split tank and it seems to be helping.
However I now have 2 more fish I have kept in the same kind of 1/2 gallon tanks I used with my first fish. The third one is in the same exact tank I had for my first one and he has had NO problems at ALL. I've had him for about 2 weeks. The last one I bought is in a brand new 1/2 gallon tank and has developed the same streaks on his bottom and tail fin. I bought him a day after the third one.
ALL items in ALL tanks in ALL situation were rinsed thoroughly and no soap was introduced. ALL water was treated with water conditioner and  temperature is maintained. I have thermometers in my tanks to make sure. I have several KINDs of water conditioner but it doesn't seem to matter witch one I use, I have the same problems. I also bought BetaFix(told it was the same as BettaMax) to use as treatment after initial doses of yellow medication however it smells and doesn't seem to help. All my tanks also have a small amount of salt added to them. I am sooooooo confused and I love my fish.
I am getting different advice from different places and I love my fish and want them to stay pretty and healthy. Is there anything I can do to prevent this problem. Could it be my water? Heck I'll buy BOTTLED water if I have to! My first fish traveled a lot with me and did well even under some unusual conditions. Except for a short bout with Ich, the first week I had him, he did VERY well until I started to keep him at home all the time, when he developed the red streaks. All my fish are very active and except for slight stubbornness in eating on occasion, which never happens with the first one, they all eat fine as well.
Could it be the food? My first fish won't eat anything else besides blood worms, though I haven't tried Tubifix worms. Nitrate levels? PH? Should I keep them all in separate one gallon tanks? Please help me. If you have ANY questions or need ANY more information PLEASE Email me. I have hand picked out each fish and 3 of the 4 are of very unusual color and I was hoping to breed them one day. But I am emotionally attached to them all!!!!
For ANYONE reading this they are the best fishy pets. And they do recognize me and greet me when I come home. Also they all have very different personalities that I adore. Especially my first one who seems to very much enjoy his fishy companions since he no longer goes everywhere with me. And he gets very excited to see me if I haven't been around for 2 days. In fact he almost hops out of the water! He DOES do flips IN the water and he always responds to my voice. Thanks just for reading this and I hope you can help as do my fishies.
Sincerely,
Jessie D., Gabriel, Shiner(Moonshine), Sunny(Sunshine), and Jester Smile

Answer
Hi Jessica;

It could be a few things. Make sure the water is at 78 degrees or higher all the time. Bettas don't do well in temperatures below that.

It is also possible that they are injuring themselves on the plants or decorations. Bettas are known for their fins catching on things and tearing them. This will cause infection to develop.

Make sure that their water gets changed once a week or more, depending on each individual tank. If the tank has a filter, change 25% of the water and vacuum the gravel once a week. If there is no filter, change 50% to 100% of the water at least once a week, twice a week isn't too much. If the water isn't changed very often then the fish can easily develop bacterial infections. Redness indicates bacterial infections.

Remove the plants for awhile, keep the temperature up and make more water changes. Regular tap water is just fine as long as you use a good water conditioner. There is often no need for medicines when the water is kept warm and clean and the fish can recover on their own. It boosts their immune systems.

Followups welcome

At Your Service;
Chris Robbins

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