With some trepidation that there will be conflicting responses to this just as there are regarding the calculation of lighting ratios, I'll take the risk.

I recently mixed up some stronger selenium toner than my usual, for an experiment. My usual is what I thought to be 1:19, and this was, I thought, 2:9 (1:4.5). I may not have further use for the stronger, and thought I'd calculate how to dilute it to 1:19. Since math tends to make my eyes glaze over, I tried to figure it out but eventually performed a web search, where I discovered that, respecting dilution ratios, 1:19 doesnotmean 1 part toner and 19 water, but 1 part toner and 18 water; likewise, 2:9 is only nine parts in total, not eleven. So, my 2:9 is actually... well, some amount weaker than I thought, not that that makes much difference at the moment.

However, I remain at a loss to arrive at how much water I need to add to my "2:9" to convert it to my "1:19". If it helps, I could start with, say, 32 oz. of "2:9".

I will be grateful for guidance.

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