Thanks for the info.I would HIGHLY recommend AGAINST using a pool filter pump for many reasons.
1) Pool pumps are made for pools with tens of thousands of gallons of water. They are going to have WAY too much flow for a tiny in comparison 900 gallon tank. Think of sitting in a jacuzzi with the jets running. That is the flow your fish are going to have to deal with.
2) Pool pumps are almost always shaft drive pumps. Shaft drive pumps are more prone to leaking than mag drive pumps.
3) Shaft drive pumps will transfer the heat of the pump running into the tank water, they will boil your fish in a day or to of running. (Guess how I know?).
For a pump much more suitable for aquariums I would recommend: https://www.ebay.com/itm/2018-New-J...147485?hash=item1c7e4e569d:g:NAMAAOSw2gxYt8lv
I love the EC40 DE filter, I can't imaging ever running a tank without DE filter. Being a pool filter it will easily take the flow of a 1hp+ pool pump. I was shocked when I initially setup the EC40 and it did a fantastic job with a tiny little Quiet One 3000 pump.
This is my current DE filter on my 35g dirt bottom gravel capped planted tank. I believe I have a Jebao DCT-4000 pump currently.
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It is a large 20" tall big blue filter with a 20 micron filter cartridge coated with DE. On my 35g tank it initially lasted about 3 months before the flow slowed so much that I had to do maintenance on the filter. Now that all the micro fine particles from the potting soil and clay that I use for a substrate have been removed it will easily last over a year without any maintenance... this is why I recommend some sort of pre-filter, so you don't have all that debree breaking down in the filter creating Nitrates.
The EC40 would go for equally long lengths of time before requiring maintenance.
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The nice thing about the EC40 is maintenance is as easy as shutting off the pump, actuating the handle up and down several times to knock all the DE off of the filter screens then turn the pump back on. Knocking the DE off of the filter screens allows the screens to recoat with a fresh layer of DE on the outermost layer. The outer most layer (I would guess maybe 1/32") is what actually does the filtering. Everything is filtered out before the water hits the inner layer of DE.
Backwashing is easier than changing filter socks???? NOT IN MY LIVINGROOM!!!! LOL! This is one of those places where what works best for me might not be best for you. If backwashing a pool pump is easier for you than filter socks then by all means I would go that route! The filter on my pool (sand filter) takes a lot of water to backwash. Where is that water going to come from? From your tank? Or are you planning on backwashing with tap water? If the backwash water is coming from your tank what are your plans for replacing the water? From watching the dirty water flow out of the sand filter it "seems" like I am flushing 50 to 100 gallons of water depending on how long it has been since the filter was last flushed.
I'll probably use a dct 20000 for the main filter pump, and something a little smaller for the de filter. After reading about backwashing, I think that would be a good way to do water changes. Just backwash the pool filter for about 100 gallons each week, thus emptying the tank and keeping a very a clean filter.
How clear is your water with the de filter?