My Dad has tried to join me in my love of aquariums and has had a 40g freshwater tank set up for 2 years. He had about (3) Gouramis, about (7) very small Tetras, and a few bottom feeders. Overstocked a bit, but I gotta say they were thriving for about 18 months.
It's also a beautifully planted aquarium.
A few months ago his plants started looking terrible, and he lost (3) fish. The plants eventually sprung back to life.
All of a sudden his plants seemed to start to look awful again, and he's had another rash of fish deaths. He lost about (6) fish over the last week, and there are a couple others that don't seem to be eating.
We tested for all of the basics. pH he keeps around 6.7 using a CO2
tank, Ammonia is 0, Nitrites are 0, Nitrates are in an acceptable range. Temperature is around 76-77.
Should he be worried that something is suddenly in his municipal tap water that he hasn't tested for?
He changes 50% of the water each week because it's right next to a sink and easy to do. He's going to scale back to a normal 20% and start using a stresscoat.
He doesn't clean the tank glass with anything but a wet cloth, so he's not getting any cleaner in the tank.