Let me see if I got this right.
You have tetras and a betta in and 8g tank and it's cloudy.
There is a highly technical term describing that condition.
Drum roll please.
As other have stated the tetras will nip at the fins of the tetra plus not have enough space or fellow tetras to establish a pecking order. Especially if you have less then 5 tetras which I hope so in an 8g. If you only have two or three they probably will not do well with the larger picking on the weaker. then during breaks nipping at the tetra.
Only solution IMHO is to remove the tetras and put them in a larger aquarium.
I also highly recommend planted tanks to prevent the cloudiness.
(FWIW: The cloudiness itself is IMHO nitrate and (mostly) phosphates plus carbon dioxide reacting to light forming the cloudiness. Killing the lights and suspendiing feeding will clear the tank. Then resuming with less lights and feeding and adjusting so the tank stays clear but plants still thrive.) I definately would not change 100% of the water under any conditions
. But then I never change any water under any conditions as well. It is best for the tank to basically "heal" itself then be reset to the initial start up values with a heavy bioload.
still just my .02
But then it is best to get the plants (added if not there already) and thriving (if there already).