After a little more research I find that your Temp. will be okay as the Tetras and Bala sharks Temp. ranges from 72-79 degrees & the Swordtails is 64-82. As for lowering the temp. I should have stated the lowering of the temp should be done gradually. This would avoid stressing the fish as fishnutz has stated.
We run our FW
tanks at 70-71 degrees and have no problems but our fish are acclimated to that temp. But as has been posted many times what is okay for one tank may not be for another. If your temp. works keep it there as it will not cause any further harm.
The red fins if truly a hemmorage or septicemia can be helped with Maraycn, But I would try switching back to your ways prior to the problem before resorting to medications.
I do hope some of these suggestions from this group will be able to help.