Where did you get the PFS ? Had it been used before or was it brand new sand bought at a store?
BTW, you said ammonia would not accumulate over 5 hours to a level that would kill - I just reread your first post - was it only 5 hours from the time you removed the previous substrate, replaced it with the PFS, re-homed the fish, slept overnite, and found the livestock dead in the morning ? Sounds more like a full half-day to me - and I'm not so sure ammonia couldn't accumulate to a moderately toxic, but nonetheless toxic, level in that amount of time. Ammonia even as low as 0.25 ppm can be toxic enough to kill, and some test kits will not reflect that low a level.
In any event, you said you tested and there was no ammonia, and presumably no nitrite spike either, so that seems to be ruled out. How though, can the blue tint to the water be explained, other than the slight blue tint that water normally has coming right out of the tap ? I assume you de-chlorinate.
Sand was brand new "HTH Pool Filter Sand" from ace hardware. It took all day to get the fish out, clean tank, prune plants, rinse sand, set tank back up. The fish however did not get back into the tank until 2am. At that time I went to bed. My husband woke up at 7am to find the casualties.
Tested for nitrites as well and 0. No our normal tap water is not tinted. We have well water and do NOT normally de chlorinate as it is not needed. Our well water has never caused any issues before and now after a 50% wc and addition of stress coat to the water and carbon to the filter the remaining fish seem to be doing much better.
Do u use prime or safe?
Not normally, but I dosed some stress coat after noticing the problem.
I'm not into pools, so I don't know if this is a common thing, or even if it's ever done, but apparently lime can be added to pool water in order to soften it, and lime does have the tendency to turn water blueish in high concentrations.
Is it possible that you pool filter sand was somehow infused with lime, destroying your ph and making the hardness skyrocket? Know that I've never read about this before, but anything is possible.
I have no idea, but I have read that other people used this brand with no issues. Only one post I found said that they lost half their tank.