Something strange going on. Extremely high TDS in rock "curing" water

[cvrle1]

I am stumped, and can use your help with this one. I have extremely high TDS from water that is sitting in the rock bucket. High as in 880 ppm

I calibrated my Milwaukee TDS meter with proper calibrating solution to 800ppm
Tap water, I have TDS reading of 12-18 ppm (Inline TDS meter on the RODI is showing 12, Milwaukee TDS meter is showing 18)
Clean water coming out of RODI is showing 0 on inline and 2 on Milwaukee (milwaykee has +- 10ppm accuracy, so this is fine I think)

I filled up bucket with dead rock that I bleached several months ago (using bleach and tap water) with RODI water and let it be for 2 or so weeks (no salt or anything else, just RODI water). I have powerheads in there to move water around. I just took a sample to get TDS reading and got 880ppm with Milwaukee ops:

For rock, I bleached it all (about 120#) in bleach and water solution for a week, let it dry out in the sun for a week and then put it back into the bucket. I washed bucket out with hose and dried it out as well before I put rock back in. Rock was sitting dry in that same bucket for 3-4 months. Before I filled it up with RODI water there was no bleach smell.

Could bleach residue somewhere cause readings this whack? Something else? No idea what happened and why I have way worse TDS reading than tap water.
Thanks for the help