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What can fit through overflow weirs and 3/4" tubing?


Staff member
Apparently decent sized Pristella tetras, Harlequin rasboras, and small gold barbs. Ask me how I know.

I had added a few groups of small fish over time to my new drilled tank to speed up and verify the Nitrogen cycle was complete, and got worried when fish started disappearing.

I couldn't find any bodies, they weren't in the overflow section, and there were no places to jump from. Eventually I gave up but worried they were dying off and just not found.

A week or two later I decided to do some sump maintenance and I final verification, even though I didn't think I'd find anything, and removed the filter socks from the sump for cleaning.

Sure enough, I had to rescue about 8 tetras, 4 barbs and a rasbora. I didn't think they'd fit through the overflow weirs, but if they did, I didn't think they'd get pulled into the drain lines.

Most people put strainers on their drain lines, but mine didn't come with any, and I wasn't sure it'd be necessary. It almost seemed better that the large debris was trapped in the socks and not blocking the drain inlets.

I'm now debating on if I should add the drain strainers, but I may not, as it's easier to remove the fish from the filter socks than it would be catch them out of the overflow area. The fish seemed to be ok in the socks for a few days and are readjusting fine.

I also thought maybe they'd have learned their lesson, and spread the word to the fish that didn't make the original journey, but 2 days later I had to relocate 3 fish from the filter socks again. I can't verify if they were repeat offenders or making their first trip, but I'm oping this won't have to be a regular chore.

Would you try screening the overflow weirs, adding strainers to the drain lines or relocating fish if/when they make the journey again? Luckily all of the future inhabitants will be too large to pass through the weirs, but these fish will probably stay in the tank long term.

Anyone else have similar experiences?


Staff member
Yes - I've had fish go down the overflow on my 92 corner. I've also had a sizable Discus make it into an (unused) overflow box in a 210.

In the 92 corner, fish that go over are generally not fortunate. The ones that don't fit through the strainer on the durso valve typically end up stuck to it because there's not a lot of space. The ones that do, land on the foam part of the wet/dry. If they're lucky, they live long enough for me to notice them. They're not usually lucky. It doesn't happen often, but things do still get back there every once in a while.

On the 300 gallon we have an external overflow and do have strainers. They're very broad, and sit at the surface, like skimmers, which probably helps stop them from clogging.