I read the posts and saw some great suggestions. We use ducks for therapy work. I started with one pen with large stones as a base and finer stones on top hoping for better drainage.
 
I use a step2 pool with an old swimming pool pump. We work off of donations. With the filter if I run twice a day, I only have to pump pool and once a week. We have problem with allege build up towards to of pool that needs to be scrubbed when drained.
 
I live in northeast PA and winter is coming. I do not run filter in winter and we use a horse water tank heater and change water when temperature allows.
 
We have a order problem even though we wash down stones. Does not bother us, but do not want neighbors or visitors to smell. Any suggestions?
 
Any recommendations on how to improve filtering or allege?
 
Additional information.\We just added a new pen with same pool no filter. No stone yet, not sure if that was the was to go. Ground very muddy, and of course they carry mud in pool. Pumping pool at least twice a week with sump pump. Leaves some mud, but not water seems clean when we refill.
 
I am looking for suggestions on what to use for ground. We do not think sand is good, because it would get carried into pool and also wash away when we spray pen down.
 
There is little chance of finding another donated swimming filter right away. Should we consider running both filter together in both pools?
Ducks are healthy. We do rescue as well as therapy so money is real tight, so looking for cheap solutions. I can probably get more stone donated and maybe other supplies. I saw many people have mentioned using straw or saw dust, but that would be really messy and hard to clean in pens.
We do use straw and saw dust in carriers to bring ducks on visits. Winter is coming and I want to get a base down fairly quickly, but looking to see what would make best base.
 
Thank you for any help,
Neil 
www.youngsfunnyfarm.org