Yes donít buy ammonia with additives, use 100% pure ammonia. Might check with hardware store for it.
A alternative is what they call ghost feeding. You basically pretend your feeding 1-2 small fishes in tank daily, as food decomposes it releases ammonia in tank. If you can add a few ramshorn snails so they eat that waste and poop even better, snail poop is loaded with good bacteria. Feed enough so you see it showing on ammonia test at 1-2ppm reading and find the amount of food you need to add every day or two to keep it there. In about 1.5wk youíll see nitrites start to climb, about 1.5-2wk after that you should see nitrates climbing.
Then back off on ghost feeding to about half rate you started with and you should be able to detect barely noticeable levels of ammonia and nitrite and nitrate levels will continue to rise. When you see 15-20ppm of final stage which is nitrate its time to start small water changes and start thinking about getting a few fish. When you add fish etc your adding fish poop into that nitrogen cycle youíve just setup, monitor itís ammonia levels, fish poop generates ammonia much quicker because itís already partially broken down by digestive track. Increase water changes as needed.
Good thing about ghost feeding is besides organic nitrogen compounds your adding to tank it also adds organic phosphate and sulfates, there is such a thing as phosphate cycle and sulfur cycle, this ghost feeding preps those cycles as well. They are much quicker and easier to implement in a aquarium. But most people who see a brown algae/diatom surge soon after adding livestock is because they have no phosphate or sulfur cycle set up, all they setup with pure ammonia dosing is nitrogen cycle. I would always recommend if your doing ammonia only cycling start ghost feeding during the last week or so of cycling. Youíll be so much further along in having a stabile tank if you do.