You cycled the tank with 6 lbs of lr
? If so then the cycle was a small one. Judging by the 3 week time period. It may have cycled but I don't think there is enough bateria there to support the tank yet. I would keep the shrimp in there and do a longer, stronger cycle. It should not harm the lr
. Give the shrimp a few days to start the rotting and produce ammonia. The cycle should take about 6 weeks.
I believe the link you posted about doing a 100 percent water change was for curing liverock and not cycling a tank. Durning a cycle if you do a total water change then you have effectively terminated any cycle you had going. If you are referring to the curing process that may be different. Curing the rock during a cycle should be performed as a cycle not simply curing. However this thread started about questions for a cycle.