I was told by someone that fish fertilizer is good for the lawn; just use 3 tablespoons in a gallon of water and apply it to the lawn. But how many gallons should I use for a lawn that's about .3 acre? There really wasn't any instructions for that, other than to apply it every 6 weeks.
Application is 1/2" gallon per 1000 sq ft.
0.3 acre is 13,000 square feet
For 6 1/2" gallons of solution.
Add a teaspoon or two of molasses, it's reported to cut the smell if you're having difficulties with that.
In this answer I went through the math on figuring out how far fish fertilizer goes. I'll assume here for the sake of reusing that math that your fish fertilizer is 3% nitrogen (e.g. 3-3-1 or some similar analysis).
Your 0.3 acre is 13,000 square feet. If your lawn needs 2 pounds of Nitrogen per 1000 square feet (a soil test will tell you the right amount), then you need 26 pounds of nitrogen. If each gallon of diluted fertilizer has 0.001 pounds... you need a lot of fertilizer! It would take 1000 gallons of diluted fertilizer to provide 1 pound of nitrogen, or 26,000 gallons to fertilize your whole lawn.
1 gallon of straight fertilizer would make up about 250 gallons of dilution, so you'd need 104 gallons to produce the 26k gallons to fertilize your entire lawn.
If you have higher nitrogen content in your fertilizer, then you will need less. (E.g. if you have 6% nitrogen, you can cut the amounts in half.)
An organic solid fertilizer that is formulated for lawns will probably be cheaper and easier to apply...
Fish fertilizer is not intended to meet the N-P-K needs but rather to serve as a foliar amendment to provide amino acids and other organic components that conventional fertilizer does not provide. The oil in the fish fertilizer is also beneficial to both the plants and microbial organisms in the soil.
Three ounces per 1,000 square feet is virtually the same as one gallon per acre. Regarding the smell, fish emulsions are usually the culprit. Try fish hydrolysate and you will likely notice a vast improvement in the smell of the product after application.