Esther, I'm starting a new thread, in case people don't see your question in my old thread about pump height....
Esther asked if those of us who have pumps on the bottom, if our pumps have some kind of pre-filter, to keep muck from being sucked into the pump.
Mine does. It comes with both a plastic basket and a sort of foam sponge. The pond store says to throw the foam thing away, as it clogs and bogs down the pump.
While the basket keeps out most of the stuff, little bits of mostly-disolved gooey gunk may accumulate within the basket. Checking it every six months is sufficient for my needs - not much falls into my pond; the bottom is amazingly clean. (Perhaps the fish are snacking??)
The pump will, over time, get some minor debris sucked into it. So, when I clean the basket, I also unscrew the housing and hose out the inside, as well as the hoses, and check the magnet thingie that twirls around.
A sales rep told me that not many people are taught to do this, but that it will GREATLY prolong the life of their pump. At least once a year.
Also, don't know if this is true or not, but a mfgr's sales rep told me, so I guess it is true... The pump has a sort of grinding mechanism, so if little bitty things do get inside it, it acts like a kind of garbage disposal. I don't see any thing inside that would grind up leaves, etc., but there sure are lots of little bitty thingies (fish poopers) that get pumped into my bog filter, and don't seem to hurt the pump on their way through.
Don't know what brand it is (too lazy to run down and check the box in the garage), but I have both a 900gph and a 700gph running in my 550 gallon pond.