It's a lot cheaper to build one yourself! I'm sure that's what most people do. They are incredibly expensive through a retailer. Also, a 55 isn't that large. So, you would ideally aim for a tank at least held that size for a sump. I know people that run a 20 long for a sump on their 55 gallon. You can pick up a 20 long for 15 bucks and buy silicone and have a glass shop cut the prices of glass and you are good to go! I did this and the total was about 40$ ! Still running good.
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