Hi Robert,(posted 8740 days ago)I work with Poly-Toner a lot. It does not give me [Ilford MG paper] the dark brown tones it talks about on the label. So, I use it very diluted, and get a reddish/brown cast, that varies with the density of the print.
I am still working on a bottle I bought about six years ago, and the working solution seems to last 'forever' also. Have not run into having insoluble stuff in the solution - the water used probably has a lot to do with that.
There is a lot of good toning info in Eddie Ephraums book: GRADIENT LIGHT [The art and craft of using variable contrast paper.
I have a friend who is banging his head against the wall trying to get those brown tones you are talking about.
The other day he saw one of my prints and said, 'that's what I have been looking for.' Problem is, I did that one on the computer.
I think the above posts have good inf. & you might also try using warm tone paper & toning.
chris