They often put lime in the mixture to keep down odors. My city compost has a pH of 8.3, and I do not use it. In regard to potash, compost has a lot of it.

Finished compost will have a neutral pH. During composting the pH can vary widely. With temperatures that high the compost you used was not finished.
I am not sure who glib means by "they" but the municipal and commercial composting operations I have seen do not add any lime to the compost those operations make. I've not found that Peat Moss does much to change the pH of anything just as leaves (which are more acidic) do not.

Possible they are using manure as an ingredient in the compost and the farmer used lime to keep down odors in the barn. Not an uncommon practice. For the OP: 8.3 is calcium carbonate (limestone found in the typical bag of lawn and garden lime). Possibly what you have there. I would expect some movement toward neutral as it finishes, but who knows how long it would take. You can keep checking if you have a pH meter and if it stays high and seems to be affecting plants, use slightly acidified water when watering. 7.8 is not that high though, I'm not sure I'd mess with it unless you're trying to grow azaleas or blueberries.

The high K may be from the compost but also could be coming from the fertilizer you used, depending on what it is. My garden soil has high soluble K but it doesn't seem to hurt anything. And it will leach away over time in your containers.

This post was edited by toxcrusadr on Tue, Jan 6, 15 at 11:28

Some 40 years ago here the initial soil tests said the Lake Michigan beach sand I have had a pH of 5.7 and very low levels of P, K, Ca., and Mg., and my own simple soil tests showed very little organic matter. 5 years later, after adding copious quantities of organic matter the soil tests showed a pH of 7.2 and above optimal, but balanced, levels of P, K, Mg., and Ca. and about 8 percent humus.
So, over time, adding organic matter (and compost is one form of OM) will change a soils values, but unfinished compost can adversely affect what is happening in the soil and is why no one really recommends adding unfinished compost to soil, if it is not necessary.
Animal manures are known to raise a soils pH and quite possibly the compost used here was more manure then anything else.

Update: I made a few more container gardens with the still hot compost by neutralizing the high pH compost level with additional peat moss. I mixed in peat moss till the DIY vinegar pH test showed that it was relatively neutral.

This may be over thinking things, but by neutralizing the overall pH with peat moss, is it possible I have unlock some of the trace minerals & phosphorus that may have otherwise been locked up? Or, will the nutrients still be locked up because I didn't essentially change the compost pH level, only the potting mix that is in?

Thank so much!

overthinking.

I'm hoping Lloyd will chime in here, but if you got 'compost' that was at 140 degrees, you are a long time away from being able to use that. I promise you what you won't be able to sprout anything in that stuff.

Do an experiment - try sprouting radish in a pot of just peat moss, and a pot with the 'compost' mixed in. See if the radish seeds germinate in the 'compost'.

Yeah, much more of a problem here with the unfinished nature of the compost than there is with the pH of it.