Hi Michael.
Welcome to the Village and to the world of scrolling. It sounds to me you got the idea of how much tension to put on the blade(by the sound). but if the blade breaking sounds like a gun going off you may have a bit to much tension. When you pluck the back of the blade with your finger nail you will hear the note. If they are snapping shortly after starting to cut, my question would be are you pushing to hard and to fast. Let the saw do the work slow steady feed pressure. to much pressure and the blade will bow and flex and cut on an angle and going to fast won't let it clear the wood and overheat, both will cause to much stress on the blade causing it to break.
I don't think it has anything to do with the wood. I cut lots of poplar. My advise would be to get some different blades, most of us use Flying Dutchman blades or Olsen. Here is a link http://www.woodenteddybearonline.com/x/home.php?cat=87. they sell both. I personally use Flying Dutchman blades. I rarely cut at full speed on my saw. most of the time just a little more than half way, all depends on what I am cutting. This is my advise/opinion I'm sure there will be more members adding their advise soon.
Does your saw take pinned ends only or will it take plain end blades too?
Don't get frustrated just take your time and keep practicing, we all started there.