I use several sized aquaclear HOB filters and find them to be flexible and reliable. for a 30 gallon, you can consider getting a AC50 rated for 200 gal/hr which would filter your entire tank 6 times each hour.
Ref Lnky: http://www.amazon.com/AquaClear-50-P...uaclear+filter
Generic fluval edge prefilter sponge - used to cover the intake of the Aquaclear filter.
Ref Lnky: http://www.amazon.com/Pre-Filter-Spo...uval+prefilter
If you want to save some $, use some stockings or an old net. Ziptie it to the intake tube.
Even though people have had success raising shrimplets without special foods, i personally recommend feeding baby specific shrimp food to increase their survival rate, moreso in an immature tank.
Regarding your dwarf water lettuce, you might have insufficient light. Duckweed will also tend to shrink and die when there isnt enough light...
Last tip for the day, the API master kit does not come with the GH/KH test. you'll have to get that separately. Its one of the necessary test kits you'll need for keeping caridinas.
Nice tank scaping...