so i was watching my fish and they are all opening and closing there mouths rapidly what should i do im fairly new to aquariums its not over crouded there are 2 young turtles in with them could it be cuz of all the poop i do weekly water changes all the fishes are doing this rapidly i want them to be happy and will buy what ever i need to to fix this please let me know ill choose best answer also my water is fairly soft between 6.2 and 6.6 how can i make it harder its a fresh water tank

they open and close their mouth to move water over their gills

As Far as the Hardness you can but powders that you add to the water to increase the hardness.
Many fish, as stated before, do open and close their mouths to pass water , or to taste foods/ smells in the water.

Depending on how often they do this , it could just be normal fish activity, i had 32 large mouth bass one year and they regularly would do this. sunfish and catfish also are known to do this. If it happens once every couple hours i wouldn't be worried greatly. If this happens to an individual fish every Couple min CONSISTENTLY there may be need to check the water quality and contents. Fish will open and close their mouths multiple times in a row.

Also , How often do you feed the fish, are they well fed?

Is the Water Properly oxygenated?

It could also be Nitrate or Ammonia Poisoning.

Bring a sample of your water to a local Pet Smart. They typically do free water testing.

I hope you find this helpful.

If you need to contact me for more information feel free.

~ Dan B