i did a little surfing on the web. This is what I found. I hope it helps.
How to prepare a concentrated solution if it isn’t in the chart below: Since the proportions at 1:16, under normal conditions the concentrated solution should be made at 16 times the recommended rate. Example: If a fertilizer recommendation is 2 TBSP per gallon for hand watering, you would make the solution at a rate 16 time greater than the 2 TBSP rate (i.e. 16 x 2 = 32), so 32 TBSP per gallon would be the concentrated rate. When mixed with water from the hose, the solution will come out the hose end at the recommended rate of 2 TBSP per gallon. The syphon mixer will draw one gallon of concentrate in about five minutes and this will be mixed with approximately 12 to 18 parts of water through the hose, depending on the flow rate. A larger diameter hose, i.e. 5/8” instead of 1/2”, will give a larger flow rate. Excessive back-pressure will cause the siphon to stop drawing. Adjustable nozzles should not be used or should be wide open for best results.

So with all that said. The answer to mix (1 Gal. @ Rate of 3/4 tsp. is .75 x 16 ) would be 12 tsp per gal. x 5 gals. = 60 tsp. for 5 Gals.

Hope this Helped. Rich