Questions about a DIY sump


New member
I'm currently building a 20g sump for my 90g tank and I was wondering how full i should fill it. I know I'm not supposed to fill it full to the top but I'm not sure to fill it 2/3 or 3/4 etc.

I'd also like to know if it is better to use bio-balls or a filter sock. I've heard contridicting opinions about both.

Is it ok for a protein skimmer to be in beside the return pump, or should it be farther away from it? As you can probably tell, this is my first sump that I have ever built so any help is gladly appreciated.

My plans for the tank is for now a FO, but after the tank has been set up for awhile, I'm going to slowly convert to a reef.


New member
It depends on how your overflows are setup and how much water can possibly drain into the sump. You could do some experimentation with the water level to see how much room you'll need for the extra water. I get about 5 gallons or so added to my sump from my overflow and display return back siphoning. I also have a 90, but a 30g sump.

I have my skimmer in the drain portion of my sump (far left) and the return on the far right. I have no bio balls or socks in my sump.


Premium Member
Best way to check for maximum water volume is to do this. Fill the tank until it just overflows into the sump. All pumps are off right now. At this time Fill the sump all the way up. Turn the pumps on and see where your water steadys out in the return chamber. Mark this spot with Sharpie or tape or something. This is now your fill line. Whenever you add top off water or do a water change, make sure to not go past this line. You already know what the results will be if you do. Wet floor. Good luck on your project.


New member
It took reading GrandeGixxer's post twist, but I got it. He is correct!!!!!

As for BioBalls of filter sock. Either is fine for fish only. You can even use them together. Filter sock draining onto BioBalls.

In general, it is best to get the best protein skimmer you can afford. That is the best way to filter salt water, wether for FO or reef. I recently built an awesome skimmer for only about $150. It blow commercial skimmers in that price range away.

Check the last page or two of this thread.