gonna take tetras back to store
so are you telling me to just take all fish out and do a 100% change and put them back in and it'll be ok???
As the other members have said, you don't want to be taking the fish out to water change; that would stress them out!
It will make everything ok
for the moment.
They way it works is this; fish produce ammonia all the time; not just in their pee and poo, but also as a by produce of respiration. When your tank is cycled, you filter bacteria will eat the ammonia turning it first to nitrite, and then to nitrate, which you remove through weekly partial water changes. Until your filter has those good bacteria living in it, the only way to stop the ammonia and nitrite building up and poisoning the fish, is to remove it yourself with large, daily water changes.
I know it seems scary, and you're worried about stressing your fish (some fish shops also confuse the issue, by telling people not to do water changes and to allow the tank to 'stabilse'; that 'advice' is a good 20 years out of date!), but big water changes are your best friend right now, and will be the only thing that will keep your fish alive.
Just make sure the new water is temperature matched (just roughly; a degree or two either way won't hurt) and dechlorinated and your fish will be perfectly alright; it's far better for them to have the small amount of stress that to be living in toxic water, as lock_man has so clearly explained.
Until you can get the water tested, or get your own tests, which would be for the best, then yes, you'll need to change as much water as you can, every day.