I have similar problems, I just did a 50% water change the other day and lost my last Briggs. They are more sensitive IMO. I have had the same nerites for 2 years or so and they are thriving, just the Briggs are problems. Is your water softened with NA or K? Also make sure your water is gassed off fully before it goes in. My water ph is 1.0 point lower coming out of the tap. You really have to let it sit overnight to get the ph to tank level.
If you can't keep them, might want to try nerites. They come in some nice colors too and kick *** with the algae and diatom.
If you can't keep them, might want to try nerites. They come in some nice colors too and kick *** with the algae and diatom.