Thank you all for the tips and advice so far.
I thought the issue had passed, as I hadn't had signs of issues for a couple of days, however, it looks like another one is on the way out. Here is a video of the fish, it was vertical at the surface bobbing up and down, now it is kinda drifting around near the bottom. I after several seconds I panned over to the fish that appear healthy (to me), maybe there are some signs/hints here?
EDIT: about an hour later after recording this the fish was dead on the bottom of the tank
, this is the 2nd that we've seen before it died and in both cases they died very quickly after we noticed.
Ph is a little high for cardinals unless they are tank bred specimens. If you are using co2 you can increase it some and that will lower Ph. The big culprit to me is the Excel and that big WC. The temp is a little low but not enough to kill tetras. Keep a log book on your water chemistry but your readings looked ok other than Ph.
When things are going good in a tank keep your changes small. I did a mistake a few days ago and increased my co2 too much and Ph went from 7.2-6.6 and my Crypts did not like it one bit.
Ph has been high, higher in fact, for most of the Cardinals lives, so I don't think that high ph specifically would be the culprit for a sudden die-off, though it is possible that changing ph could be a culprit. I changed from hard alkaline tap water with high nitrates to remineralized RO water over the course of several weeks with 30% water changes every couple of days. The ph of my remineralized RO water is around 7.6. The tank was stable for about a week with no additional water changes before adding the shrimp and Excel, and the next morning, 4 dead fish. I could of course chalk up the timing of the dead fish and Excel to a coincidence... but for several weeks with these aggressive water changes I didn't notice any signs of stress with the fish until the morning after the shrimp/Excel.
As it has already been stated dead shrimp are not normal during shipping. Your water is too cold for Cardinals. They are a fairly sensitive fish.
I have dosed excel in low tech shrimp tanks for years and have sold hundreds of shrimp out of said tanks. Excel does not (in my experience) effect neos or amanos.
Has you water parameters always been this way? How long has the tank been set up? Are you dosing ferts? Also poke around your Substrate with a shish cabob stick. Sometimes gasses get trapped. Just some ideas. And sorry if these have already been addressed and I missed it in the other posts.
Sent from my SM-G920V using Tapatalk
See answer above regarding recently changed water parameters. Based on your advice I will increase the temperature of the tank. Tank has been set up with cardinals for about 6 months. I am not dosing ferts. I'll give poking the substrate a try to release gasses.
Dead shrimp in a shipment is not normal unless you are talking warmer water shrimp who were left in child weather for way too long.
This doesn't help with Amanos jumping ship, but could the RCS have had a bacterial infection or something similar, and it was passed on to the fish when they snacked on dead ones?
Sent from my Nexus+6 using Tapatalk
I was also concerned about an infection from the shrimp, however both the seller and my LFS said it would be extremely unusual for an infection like this to have such a quick overnight impact on other inhabitants, if it was an infection they said it would typically be a much slower process to infect and kill the fish, do others agree?
I have a lid, though there is a 2" gap in the back. I read through the article linked above and I'm racking my brain to think of anything we have been doing different in or around the room the fish are in, I can't think of anything we have a pretty consistent cleaning regime, so I can't imagine anything new that would cause a sudden dramatic issue, but we will be extra cautious considering this going forward.
Thanks again for your help so far!