How Much Ammonia, ( Back On The Cycle)

The original method of fishless cycling used 5ppm; I don't know why they chose that figure but it has stuck. You'll still see 5ppm on a lot of sites. But a fully stocked tank makes less than 3ppm per day so if you grew enough bacteria to remove 3ppm in 24 hours, you'd have more than enough bacteria.
But as you don't want to stock fully once the cycle is finished you can add less ammonia. If you think you'll stock to half full, use 1.5ppm; for one third full, use 1ppm. That's the smallest I'd go with. Even if you only stock to a tenth you'll have enough bacteria and that's all that matters.

As for how much ammonia to add - if the bottle of ammonia is 9.5%, for 1ppm you need 0.11ml for every 10 litres.
260 litre tank, subtract 15% for substrate, decor etc leaves 221 litres. Call it 220 litres. The dose rate is 0.11ml in 10 litres so you need 2.32 ml ammonia solution to get 1ppm in your tank. Assuming it is a 9.5% solution. Test for ammonia half an hour after adding it to check.


To seed the tank, carefully lift the media out of the 90 litre filter, open the new filter and squeeze the media out above the new filter. You want all the muck to go into the new media. Then once you have closed the new filter and put the media back in the old one, add the ammonia. I'm suggesting using squeezings rather than actual media as the old tank hasn't been cycled very long and you don't want to upset the old tank.