Water changes,and check temp's as weather warm's also.
Most all issues in glass box of water are negligible with regular water changes ,maint.
If you don't know what's in your water,use good all purpose Dechlorinator like PRIME.
Most effective if chlorine,chloramines,metal's are at unknown level's, and last's three times longer than all other conditioner's per ounce.
Will get a feel after a few month's as to how long between water changes, and how much should be changed.
Take care of your water,,,and fishes will be much healthier,happier,longer.