I would open the filter back up and if it’s still blue, suck it clean with a shop vac. Then soak the filters overnight in a 50:1 MA bath. I’d check it in a day, then a week, then a month if it didn’t return.
The pex is embedded in the concrete under the liner, and no. I us Uponor/Wirsbo, which is all pex with hard plastic fitting to the extent I need any. Normally I just bend the pex around corners or possibly use a hard plastic bend support. There's no pool water contact with the pex.
There's no chance. I was planning to install it in the filter (even though it looked pretty knarly), but then I read the N2 literature (which said dispose after 4 months and do not reuse, and also discussed the possibility of it rupturing) and I decided I was better off without it. It was ancient and looking rather decrepit. There was no marginal benefit to it's inclusion, only cost, so I put it in the trash.
I agree that copper seems like a likely culprit, based solely on the color. The problem is from where and when?
If it was from the prior Nature 2 containers (and there is no evidence that they ruptured), the pebbles would have traveled downstream from the filter (if they could get past the old filter, which was replaced) toward the pool return and into the pool. If they made it into the pool (and the gpm flow of the pump is about 30 gpm!), then they would have been discarded with the relocation of the pool. There's no evidence that the prior Nature 2 container ever ruptured. Further, since the system was disassembled after the prior Nature2 usage, any prior rupture would have most likely been dislodged in the relocation process (if the pebbles were left in the piping). If the ruptured Nature2 remained in the pipe and wasn't dislodged, then the cloudy blue water would have first been discharged first into the newly filled pool, which wasn't observed.
The source of this cloudy bluish water remains a mystery. I'll open it again at some point, but since I have a new Nature2 cartridge in there now, I think that any bluishness or cloudiness will just be attributed to the new Nature 2 cartridges (which I couldn't deny, since that's right where the Nature2 container will be, and I have no experience to the contrary). If I were to find the filter center bluish in the future, when the Nature2 cartridges are in there, I would probably even think that it's normal, as long as the color and haze remains in the filter, perhaps doing it's job in a more concentrated environment.
Since my question seems outside of the norm, and doesn't have any clear answer concerning the cause, I'll just let it go, but I'll keep an eye on it. It's not hurting the pool for now.
If there are any other Endless pool owners out there, or other cartridge filter users, who also use the Nature2 sanitizer, it would be great to hear from you about your cartridge changing observations.
wireform, The drain valve looks like it's brass, but it's actually plastic. Also, it's downstream from the filter, so it would discharge into the pool rather than accumulate in the filter. But that's a sharp eye to find that detail. I don't think I would ever see that!