looks good!
Great find.
TBH, i have never used a HOB Filter before, but i doubt it will need any Mods, and should work fine as it is in terms of flow.
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This might help, when setting it up:
Hang On Back (HOB) filters are only suitable for smaller tanks, you'll need a more powerful internal filter or external canister filter for tanks 2 ft & larger. As the name implies the whole filter usually is hung on the back tank wall. There's an inlet pipe sticking into the water and the cleaned water exits from an outlet near the top. For smaller fish & fry, you can cover the inlet point with a sponge that fits over it, this prevents fish from getting sucked up or against the pipe and becoming killed, injured or having their fins ripped.
It's possible to do all 3 types of filtration: mechanical (trapping solid particles), chemical (removing toxins, colour & odour) and biological (beneficial bacteria to convert toxic ammonia to less toxic forms). Many HOBs come with filter & carbon pads provided, which perform the mechanical & chemical filtration respectively. You could replace them with the same pads but it tends to be expensive in the long run to keep using proprietary stuff. You can substitute with cheaper alternatives, usually just a matter of cutting to fit and stuffing to ensure there are no gaps. I also highly recommend to add biological filter media like bio-rings, sintered glass etc to allow good bacteria to grow on them.
Note that HOBs are not very effective at mechanical filtration unless you maintain them well. The inlet pipe is usually quite narrow and hence the impeller (propeller like thing) can get clogged if there's excessively large stuff like dead plant leaves. The filter will not be able to suck up all the dirt, especially on the far side (try hanging it more to the center if possible); you still need to do your gravel cleaning. But on the whole a good HOB filter can be quite effective for a small tank, certainly better than a small internal filter or those older box filters driven by an air pump. I've used various kinds of filters for small tanks before and thus I can say that HOBs are the best choice for smaller tanks since canister filters are way too powerful.
For any filter, please note that it should be able to turn over about 2-3 times your tank volume per hour to be effective. Too fast a flow rate is not good for tanks with live plants (some plants may get uprooted & excessive water agitation causes necessary CO2 to dissipate) & stressful for certain fish (eg. smaller fish, fish fry, bettas, angelfish); best if the HOB has a control valve to adjust the flow rate.
~Yahoo answers
