I just found a used 70 gallon aquarium for sale and the seller said he had a diatom filter some place in a box that he would throw in with the tank. I know nothing about them. I looked on the web and saw that at least some of them could be used as a constant source of filtration in the tank. I'm trying to figure out if this is a could deal and i could actually use the filter or if it's just a waste of money. If somebody could help me out I'd appreciate it.

well the 70gallon tank is a good deal as for the filter i am not sure.

the rule of thumb for filters is 10xgph so if it 70gallons you need 700gallons of filtration an hour. you can have as many filters as you want but the overall gph (gallons per hour) should equal 700gallons or more an hour

hope this helps

Diatom filters are used to polish water (they take out the particles that your filter miss) and should only be used occasionally since their media clogs fast. If you wanted to use them all the time, you'd have to change it very often-maybe even everyday.

I agree with goldfishlover, there are some newer models that are supposed to "never clog," but I've heard a lot of the older models get all clogged up when they've been operating for extended periods of time.