Susan Erickson wrote:

Used to use this. You have to have a super saturated solution.
Mix it with hot water and add tsp until it will not dissolve.
When it cools some will drop out of solution..........
................
SuE
http://orchids.legolas.org/gallery/albums.php

I've come back to your post with another comment/question.
I agree with the above. Everyone recommends a fully saturated solution.
I do the dissolving in hot water and, as you say, as it cools some
crystallizes in the bottom.
TSP works because it raises the pH so high. (I think Arron Hicks once
said it needs to be about pH 11 but don't quote me!) More gets dissolved
in hot water, less after it cools. Does the pH change when this happens?
I would think the pH would be higher at a higher temperature because
there is more TSP dissolved. I wonder what is really happening when I
keep my batch of TSP solution in my rather cool basement. (often upper
60s and never over mid 70s.)

Steve ... who should really learn how to text pH in the extreme
alkaline range!