Cycling my 3 gallon

[Eolith]

I have recently acquired another fish that was taken in as something of a "rescue". His tank hadn't been cleaned out or had water changed in about all the time that his previous owner had him, so I felt that it would be best to empty everything out, scrub it down, and start over... which means that I'll have to do a fish in cycle as I don't have any spare pre-cycled tanks around >_<

First of all, a 3 gallon is big enough to cycle, right?

It has an under gravel filter system and one of those penn plax small world filters. (This is the one http://www.petco.com/product/3199/Pe...t=OnSiteSearch)

I have all of the liquid tests that will be needed for tracking ammonia and nitrites as they go through their cycles, but what I want to know is how much water I should change out at a time when I start to see the ammonia/nitrite levels rise and what the maximum level of each should be present (is it about .5 ppm or .25 ppm?).

Finally, would it be worth it to get something like ammo-lock to convert the ammonia into a non-toxic form while the tank is cycling? (This is the ammo-lock I'm talking about http://www.petco.com/Shop/Product.as...sultRedirect=1)

[1fish2fish]

I don't bother with any other additives except water dechlorinator.

3gallons can most certainly be cycled. I have 2 gallon tanks that are cycled, my 3 gallon was no problem.

I do a 25% water change any time I get a reading of ammonia on or over .25ppm. If I get a reading of 1ppm or more I do a 50% change.