Contrary to what you are saying one can purchase lake dyes with Acid Yellow 23. I have also heard of many complaints that the people do not like the Aquashade color, it looks too un-natural. The yellow makes it too green. You might try adding some black dye to the blue to make it more appealing and light absorbant over a wider light spectrum(Some black dyes contain yellow 23).
Regarding the "relative cost" of Yellow 23 vs Blue 9, what would you estimate the cost per kg of each?
As for the use of black lake-dyes (which appear to contain red & yellow pigments), they're often applied 50:50 in relation to half the typical dose of certain blue lake-dyes to yield a much more natural appearance. But, in my experiences with this practice, I have yet to notice any notable suppression of submerged macrophytes.
And what is the PURE BLUE LIQUID to which you referred? And who, pray tell, produces it???
