I didn't read through all the responses so I may be repeating a few. Make your life simple and put in a skimmer. In the skimmer put a 3000 gallon per hour pump or larger (water is better pushed than pulled). Push the water to a skippy filter that is at a higher level than the waterfall and the water will flow to the waterfall. A filter can be made for under $70 dollars. In the skimmer and in the filter add filter material that can be bought on Amazon for the mechanical side of the filter equation. For the biological part use plastic construction/snow fence. Add a check valve in the skimmer and another gate valve before the filter to regulate the water if needed. Use PVC piping or flexible piping but not the cheap sump pump type of tubing. Check locally for the lining because shipping can get expensive. Use an old rug for padding and if you can find one an old swimming pool liner as extra padding. Check Craigslist for all your items.