A DIY filter is fine, but I wouldn't use a pond filter for a tank any smaller than several hundred gallons! Many hobbyists have come to believe that good filtration means a lot of fast moving water. But good filtration is about how well we filter the water, not how much, or how fast, we push water through media.
And filters don't clean the water, they just make it look clearer. Filters trap detritus where it continues to decay and pollute the water!
------
I've seen it written over and over that we need 4x to 10x the tank size in gallons per hour. In a word, this is nonsense.
I've also seen it written many times that "there's no such thing as too much filtration", But YES there is. Not long ago on a FB forum I saw a 55g tank with three (3) large canister filters underneath, when one would have been more than enough! A waste of money and too much water flow for most fish to be happy.
------
There are many, many tanks out there that have crystal clear water that merely use an air driven sponge or box filter...and many more JUST USE PLANTS with no 'filter' at all.
------
So...a DIY filter is fine, but I suggest to you that most filters out there that are rated for your size tank have ample flow rates to maintain water clarity.
A decent filter, a good cleanup crew (like Malaysian Trumpet Snails), and routine tank maintenance is all we need.