water flow
Hi, I have been building ponds / waterfeatures as a hobby for 15 years and waterflow is the key. Personally one of the easiest filtration systems I have ever had is the natural one. You have the correct concept in building the 30 gallon and letting it spill over to the 100 gallon. I have used preform ponds, liners, buckets, horse troughs, basically anything that would hold water to build water features.
I love them. I currently have three features outside. I am in the process of uploading my last pond remodel. I did it by myself and it was relatively inexspensive. I did have a lot of the items needed already, but did need to buy some more liner. Sorry to ramble.
In my pond I have about a 3' x 4' upper pond and a 6' x 7' lower pond, not real sure of the gallons, but I have a 4500gph pump powering it. My waterfall portion is 2 ft across. It is a mess right now due tot he winter, however the water is crystal clear and my fish are happy. My upper pond is filled with water hyacinths, and iris....and a few, ok a lot of weeds.
. But the point is all the water has to go through their root system which is massive and it keeps the water clean. It also allows for a large amount of water to pass over my flat rock used as my fall. Ok... If this works here is the latest one I built. I live pretty close, feel free to pm me your phone number and I can call you to answer any more questions or help in any way. Ohh... this is not my business or anything just a hobby.
http://s163.photobucket.com/albums/t308/Saltwatersilly/