Okay I am resurrecting this old post so I don't have to type out all the background again. Not long after I posted this I got sick and so both of my tanks were kind of neglected. They did not get the water changes as often as I usually do and I didn't get any of the changes made to the 10 gallon tank with the pygmy cories, endlers and red cherry shrimp that were talked about in my original post. Finally I am feeling a little bit better so went ahead with the changes previously discussed when I initiated my question in April. I have the 3.5 gallon tank that they previously occupied and moved the endlers and pygmy cories out of the 10 gallon into the 3.5 for their temporary home. The corys are so good at hiding that I thought I only had 1 or 2 left but once I got all the stuff out of the tank I had all 6 corys left that I had started out with. Sadly I lost all the cherry shrimp - probably because I did not keep the tank up to its usual level of clean. I put a little gravel in the bottom of the temporary tank, some plants and moved the cycled HOB filter from the 10 gallon to the 3.5 gallon. I took all of the cholla wood, plants, marimo moss balls and fake rocks out of the 10 gallon and put them in a bucket of tank water. What a job it was to get all of the gravel out and that undergravel filter. I was kind of shocked about how nasty the water was under the undergravel filter. I took the aquarium to the sink and hosed it out really well and did not use any cleaners or detergents - just elbow grease. I put in the black sand which I had washed, installed the sponge filter as recommended, put the plants and cholla wood and other décor back in. I am still recovering so all of that took me two days because carrying the water back and forth is just exhausting for me right now although that will get better with time. The sand is mostly settled - how long should I wait until I move the fish from the temporary tank back to their newly redesigned home? I will move the cycled HOB back too but eventually just want one filter on there so about how long will it take the sponge filter to build up an adequate bacteria supply? Now that I am feeling a bit better and can do my tank maintenance now I do want to add more red cherry shrimp. Should I give the tank some time to settle before adding them? I was thinking maybe wait 2 weeks. Also before I took everything out there was a lot of water movement in the tank - I had the 2 uprights from the undergravel filter, the HOB filter and a 12 inch airstone buried in the gravel. I ready that cory cats come from slow moving water. Right now all I will have will be the sponge filter which is one of those that has 2 arms on it with the sponge and a discharge between them so that creates some water movement. And the HOB filter moves some water too. Is that enough water movement? Don't want the pygmy cories to have to fight too hard to swim. Wow I am long winded!! I always appreciate the information I get here. Thanks in advance for any responses.