I agree this would probably work OK from a pure filtration standpoint if the filter is totally cleaned and has no chlorine residue. A bigger concern might be that the flow rate for even the smallest swimming pool filter is going to create a maelstrom in a 150 gallon tank unless you are very careful about your intake and return piping so the flow is spread out over a wide area (perhaps pipes with many small holes drilled in them ?). Pumps designed for a particular flow rate don't like to be throttled back to just a small fraction of their rated flow. Also, a lot of the electrical energy you'll be putting into that pool pump motor is ultimately going to wind up heating your tank water, particularly when the pump is throttled back. This might create so much extra heat (think in terms of a 1/2 or 3/4 horsepower pump = two or three 200 watt tank heaters being on continuously), vs a 150 gallon tank's surface area getting rid of that heat, that you'll need to add a chiller to avoid potboiling your fish when that big pump motor has been running for extended periods.
My gut reaction is that although the pool filter might seem like a cheap alternative, given the possible complications you might be better off going with a filter system which is better matched to your application. Operating costs are also an issue. Even At 10 cents a kWh, running that big pump motor is going to add up to say .4 or .6 kW * 24 * 365 * .10 = $350 or $500 per year in electric bill. With that kind of money involved, you could spend $250-$350 on a better matched filter system with a smaller pump costing much less to operate, avoid the maelstrom and tank heating issues, and still be ahead of the game financially just one year down the road. Going with the 10 turnovers per hour rule of thumb, the right sized pump would be rated about 1500gph. Mag drive pumps in this size range typically have motors which are 1/6 hp or so (Danner's 1800gph pump uses 145 watts). Thus you're talking an annual electricity bill of say $131 instead of an electricity bill three or four times that high with the big 1/2 or 3/4hp pump motor on a pool filter running all the time.
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