Which fish should I get

[KatNor21]

Please always post numbers. The tap water was "hard" and now "soft" is meaningless without the numbers.

When testing pH of tap water only (not tank water) you need to ensure the CO2 is out-gassed or the result can be much different (and inaccurate).

Yesterday, my tap water was GH 25ppm. Today it is 300ppm. Same method, same faucet. Tested the tank too and it was 50ppm yesterday and 300ppm now. In case you'd want to know, KH is about 40 in both and pH about 6.5.

How do you "out-gas" the co2?

 

[Byron]

Yesterday, my tap water was GH 25ppm. Today it is 300ppm. Same method, same faucet. Tested the tank too and it was 50ppm yesterday and 300ppm now. In case you'd want to know, KH is about 40 in both and pH about 6.5.

How do you "out-gas" the co2?

The GH of the tap water is determined by the source water (reservoir, lake, whatever). The water authority might add calcium/magnesium. And the source water may be subject to fluctuations between seasons. I would check with the water authority on all this to pin down exactly what is occurring. What are there readings, what if anything do they add.

A related GH issue would be a water softener/filter unit in your home. One would expect this to lower the GH, not raise it, but I mention it.

As for the GH in the aquarium, this will normally match the GH of the tap water. Organic decomposition can lower it, as can plants, but I cannot see this being so great as 300 ppm down to 50 ppm in one day. Calcareous substances in the aquarium could raise it however.

To out-gas CO2, let glass of fresh tap water sit 24 hours, then test the pH. The CO2 dissolved in the water will lower the pH, by forming carbonic acid and binding to minerals; once out-gassed, the pH will return to what it is in connection with the GH/KH of the source water. The water authority may add something (like soda ash) to raise the pH, so again see what if anything is being added.

 

[KatNor21]

OK, I got an API GH and KH kit, tested pH as well with my API bottle. Also let some tap water sit for 24 hours (same faucet I use to water change, and there's no filtration or anything). Here's what I found.

My tap and tank water have the same GH of 7 degrees (100-200ppm) and pH range is 7.2-7.6. Seems my water here is indeed hard. The neons have been relocated and I'm changing my plans for the tank.

 

[Essjay]

7 dH = 125 ppm. Are you looking at the table which says which fish are supposed to be suitable for which hardness? It does say that 6 to 11 dH = 100 to 200 ppm. (Take that table with a huge pinch of salt, it's too soft for the fish they suggest in that band).

7dH/125 ppm is soft water not hard water. It is suitable for neon tetras and other soft water fish but far too soft for hard water fish.

 

[Byron]

Following up on @Essjay post, I previously suggested you contact the water authority to confirm any substance they might be using (other than chlorine or chloramine), just to get that issue resolved either way.

The other issue is the Fluval stratum, that I earlier suggested might be affecting parameters. It would be advisable to test periodically but regularly to see if the tank water changes. GH (I wouldn't bother with KH here) and pH are both important. Every second or third day is fine. Keep in mind that pH does fluctuate every 24 hours, normally, so test GH and pH at the same time of day each day you test. The pH first thing in the morning after the tank light is on will be lowest, while the pH at the end of the day when the tank light goes off will be highest. Write the test results down so you can refer back over a period of days/weeks going forward.

You have soft water, so fish in post #1 are OK so far as parameters are concerned.