Cycling is the tank growing benifical bacteria to help with the break down of bad bacteria (fish poop, and uneaten food) in the water.
When you fist set up your tank you will need some bad bacteria to get the process started. This is why most people use a jumbo shrimp from the grocery store. It will start to decay in your tank and there is the bad bacteria that you need to start the process.
Then there are the fish stores, only out to make a buck. They don't care about the live or health of the fish. They will sell you a fish to start your cycle. via fish poop, or as the fish gets sick and/or dies. That is not needed, and is cruel to the fish.
Take the cocktail shrimp and place it in your tank for a day or two. As it starts to get mushy and ugly take it out. At this time if you check your water you should have a high amonia level. This is when the tank will start to produce NITRITES, nitrites will then break down the amonia and turn it into nitrites. The amonia level will then start to go down. and the nitrite level will then go up. Then the tank produces NITRATES. Nitrates then break down the nitrites and turn them into ntirates. All the while your tank will be building up good bacteria. By this time there should be enough to start breaking down the nitrates. The good bacteria will break down all the nitrates and the all test should show zero readings. This process should or could take a few weeks. But that is how nature works! After about three to four weeks your readings should be: amonia - zero, nitrite - zero, nitrate - zero. Once you are at that point then it would be good to do your first water change. Change 10 to 15 % . Wait a day or two then you can add your clean up crew. A few snails, hermits or shrimp if you want, give them a few weeks before you add anything else. One thing to remember, Your tank will have a load of good bacteria to handle breaking down the bad bacteria in the tank. But it is not instant. And anything and everything slowly, so the tank can adjust to handle the extra bio load that each and every thing in the tank will add to the load. If you add thing to fast, it may be more than the tank could handle, and your tank could crash.
As far as the damsel go, you are best avoiding them from the start. They are inexpensive for a reason. They are very mean little sh*+s. And once in your tank very hard to get out. And most people do want them out at a later date.
