Troy, The floor of the pump house is one foot below water level. It does have a concrete floor with a drain in the bottom. The walls are concrete (a person could use cement blocks) up to ground level with small anchor bolts in the top to bolt a wood pressure treated plate for the top part of wood. The structure is about 46" x 46".

After a little research I found a website, linked below. It appears to have a chamber for oil. Unusual for a sump type pump of that size. You normally don't have that until you get in to the higher HP range. I'm impressed that it would have that feature. It is there to lubricate and to protect the motor from damage if the bottom seal goes bad. It may have a bad seal between the motor and the oil chamber, and/or possibly the seal on the bottom. Most likely the bottom seal. If the bottom seal is bad it will push water into the oil chamber due to water pressure from the impeller, forcing the oil into the motor. Which will trip out a GFIC. The oil will come first since it will rise to the top. Once the oil is all pushed out the water will come in. "Is the pump toast or is it fixable?" It's a crap shoot, probably fixable, but probably not worth the time and money. Another note to mention, in case you buy another one, is the first reply on that site, " What no one will tell you is that this manufacturer recommends that the lubricating oil be replaced every 6 to 12 months" Here is a link that might be useful: pump

My pond is about 1800 gallons. I designed and dug it myself. I use a submersible pump. I wish it was out of the pond, and here is why: I have to enclose the pump in a filter "sock", to keep debris out. That filter periodically needs to be washed off, which means raising the pump and attached, bulky hose, opening the bag and hosing off the filter material. Then reassemble and replace. I have to perch on the side of my pond to reach the pump and in the middle of summer with everything growing and rocks slippery, well, it isn't ideal. Maybe it's bad design on my part, but I find it cumbersome to maintain. I did it this way to keep expenses down, and it certainly is quiet, and hidden. And it works quite well. I just don't like the upkeep. If I had the option of a contractor installing it, I would request the easiest upkeep method and pick the pump for energy efficiency. There is a big difference between pumps as to how much energy they draw. Do your homework there. Hope that helps-

I guess that if your pond depth is really 3.5' that your volume may be correct. In any case, 900gph is way low for the generally suggested ratio of flow to pond volume. BTW, I have an auxillary pond that has no flow. It can be a total mess of muddy water after a big rush of accumulation from our French Drain. However, this crud will precipitate and this catch basin will become completely clear, again with no pump! I have been very lucky and never had pea soup type issues. I am assuming that this is what you are referring to and not just some string algae, which is a good thing anyway. You failed to indicate your location or garden zone. It may be useful information. I hear that ponds without much plant cover are more likely to get algae problems. I suppose hotter brighter conditions increase the problem. My aux. pond (without any flow) is in the woods with minimal sunlight. There are plenty of in pond pumps that work fine. I don't actually understand where your crud that restricts flow is collecting. I have a 2500gph pump contained inside its own overall slitted case. I remove leaves and other crud that get sucked to the surface every few months. Perhaps your pump is so close to the surface that it catches most of your leaves? Perhaps at the bottom instead, right where leaves fall? BTW, the bottom is not the right place for a pump because a big plumbing leak/break will drain the pond.