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Help with fishless cycle

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In early April, I started up a new 90G tank and began a fishless cycle using Fritz's ammonia (made specifically for aquarists doing this sort of thing). Two months later, I have not achieved an ammonia reading of zero and I'm wondering if this community can help me to understand why, and what to do differently. More details below:

1. Tank Details - 90G aquarium with two Fluval 406 filters. There are no fish in the aquarium as I am waiting for 0 ammonia and nitrite, however there is some driftwood and a variety of low tech plants which are doing pretty well aside from some normal crypt melt from shipping.t
2. Cycle details - I dosed the ammonia as directed to bring the tank to 4.0ppm ammonia. I tested, the next day and my levels were in fact 4.0 ppm which rules out that I overdosed. For 5 weeks, the tank hovered between 4.0 - 3.0ppm. Because the drop was slow, I did a partial water change thinking the tank needed a nudge to cycle thru those existing levels of ammonia. This brought my ammonia to what looks like 1 - .05ppm. Now, 1 month after the water change and 2 months after starting the cycle, my ammonia seems to be in stasis at .05ppm and is not moving.
3. Other - I of course dechlorinate the water before putting it in the tank knowing that the bacteria won't grow in chlorine. Also, when I test the water out of the tap, there is 0ppm Ammonia.

What do you think I'm doing wrong? What should I do next? I'm confounded and pretty weary of the struggle (as are my poor kids waiting patiently to buy fish), so your advice is much appreciated!
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You need to maintain ammonia at 3-4 PPM for the duration of the initial 'cycle' process. Which means you'd need to dose it somewhat regularly to maintain that. That ensures your tank's filtration system (the entire tank) can process a fixed amount of ammonia so you can add all your livestock at once.

Doing water changes didn't help. Dose back up to 3-4 and keep it there. Once you can process that amount within 24 hours or less and have no nitrite reading - but do have a nitrate reading - then your tank is ready. If your livestock is ready to move in or you'll be adding it the next day, do a 100% water change and move your critters in. If not, then continue dosing to 3-4 PPM until you're ready.

To give things a boost, you could consider adding a bottle of bacteria. I think it'd probably be a waste of money, really, as your tank is already processing some ammonia. Which means you're half way there. Could also consider adding some filter media or some such from a friend's established tank (if that's possible.) Otherwise, it's just a waiting game. Keep that ammonia steady so bacteria can build up.
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