Gee, it sounds like you are using it way too concentrated. To do my 6.4m hardtop, all over, I would top the dispenser up twice. I just went out and measured some into the dispenser to give it the colour I would normally start with , and it took 15ml in a 90 ml dispenser. See picture. That is of course constantly diluting as you use it, so, when it gets really pale blue, I add maybe 10ml to it to finish off. So I am using maybe 25ml a time. But less really, as I just look at what is left when I am finished, and add as required next time. Reading Saltaway's product information, they say that in lieu of measuring you just need to be able to see that the dispenser is looking a shade of blue. Even using it as a detergent with a soft brush to clean off baked on dust and salt accumulated over a month of use away from freely-available water, I wouldn't be putting it in that dispenser full strength. Maybe half full.
I bought a dispenser sold with a 4 litre container thinking it was the genuine thing and it would dispense constantly agt the recommended rate. WRONG. It was just the base part of the Sabco type I posted above, moulded in different colours, and branded A-salt. All parts interchangeable.
it does have the advantage of having a clear dispenser, vs the smoke coloured one on the Sabco, so its easy to gauge the dilution. So that now lives on my outboard flush attachment, and gets some saltaway when I feel like it. When I am using the boat almost daily, I don't add any, but after a long time away from flushing facilities, I'll give it a run. And saltaway do say not ot leave it running--start with fresh, get a flow, then turn on the saltaway until it starts to foam out the telltale, then stop. So you are using very little in that scenario, too.