DIY rock question

[SmallFry]

Hi, I need some input on the leaching out process for my rock...

I've had it in a rubbermaid for quite some time, and for the longest time it would punch the pH up off the scale on my test (anything over 8.8) within about a day of adding fresh water. Sounds bad, but bear in mind that once the rock was in the rubbermaid there was only room for about 15 gallons of water to about 55lbs of rock. Recently it started to slow down a bit, and I got my 75G plumbed, so I put it in there to get the benefits of more volume and some circulation. Well, soon after adding it the pH was up from 7.something to 8.2ish (I know that sounds vague, but those colours are so subjective). So I thought it was still curing, but it's now been in there for a week and the pH is still pinned at 8.2.

Does this mean my rock is ready, or not? I would have thought with the pH not increasing over the week that would mean yes, but the first hike up to 8.2 has me questioning that. The only thing I can think of is that aquascaping broke some bits of rock a bit and released some more stuff into the water. Perhaps upending a three 5G jugs of water into the rubbermaid was having a similar effect in there too?

I think I'll just leave it to run in there for a while longer, after all, I can't get things started until I've got a light sorted - so it's got as long as my LED build takes..

I've also noticed something odd with my high range API pH test too. If you leave the water you just tested to be 8.2 overnight instead of throwing it away, it magically turns into 7.4? Anyone else noticed that?