I have a reef octopus return pump that uses a float switch too and shuts off when the water gets too low, however in this situation the water would get too low but then come back up due to the auto-top off, triggering it to turn back on.

My pump is compatible with the apex though, i assume i could set it up so that once the float switch is tripped if stays off indefinitely until I turn it back on?

I agree with you that it would probably be more likely to clog by small debry, and probably less likely to clog due to something big like a turbo snail.  I guess if I clean it often though that wouldn't be a problem?

I do have one other flood scenario that i'm not sure how to fix.  Maybe one of you has planned for this or thought of a way around it?

Imagine if both overflow pipes were to clog, the return runs out of water pretty fast and there isn't enough water in the sump's return pump section to overflow the display.  However the auto-top off will turn on in this situation as it monitors the return pump section's water level.  I have a Tunze auto-topoff that has some safety features.  I believe one of the features is that it won't run for more than a set amount of time.  But in the case that this failed (i know i know, 3 things failing all at once is unlikely... but can't be too careful) is there a way to stop the auto-top off from running indefinitely until it runs out of water in the reservoir, flooding the display?

I am setting up a new 90 gallon and just finished all of the plumbing.  I have tested every failure scenario I can think of so far to make sure I can't flood the place and so far so good:

main overflow clogged

backup overflow clogged

both overflows clogged

power outage

power outage with check valve failure

power outage with snail parked on syphon block

power outage with snail parked on syphon block and check valve failure

....you get the point.

My question is about the backup drain pipe.  It sounds like most people leave this pipe wide open at the top, but I was hoping to add a strainer to the top of this pipe to prevent a rogue turbo snail from clogging it.

I was planning to just snap this one in place with a slip to thread fitting (without glueing it), so that I can easily take it off an rinse any debris off.

Is there a reason not to do this and to use an open standpipe instead?  It seems like everyone in the community uses a plain old open standpipe so I was curious if there was a reason why?