Red Sea weir overflow

esprits300

New member
Hello, I recently purchased a Red Sea max nano g2 XXL and set it up. I have the Red Sea nano mat, and a reef wave 25 in it. I have 1 question and 1 problem. so I have everything setup normal according to the manual, nothing fancy. everything has been running for about a month or so but the watch catch box behind the weir overflows constantly. not a lot, but it does flow over the whole length of it. the tank is an AIO and the weir has 2 outputs. one goes directly into the nano mat, the other dumps into the rear "sump".

I cannot for the life of me figure out why the box is overflowing. I have an ATO with auto sensor (Red Sea) on it and I know its level and correct. at first I thought the surface agitation was too much and pushing it over so I turned off and redirected my output heads. that made it better but didnt make it go away. turned off the reef wave as well. ive cleaned the weir and all equipment 3 times. when I put it back together and turn it on it takes anywhere from 10 minutes to 30 and it starts overflowing again. I thought the nano mat was dirty so ive used all new floss on it. nothing. no matter what I do, it just overflows. anyone heard of this? this is my first large tank, ive had a 33, 32 and a 20 prior but they never had this issue. ive contacted Red Sea but I get the feeling im going to get ignored.

which brings me to my question. so the second compartment dumps directly into the sump area. no filter no nothing. just spills into it. by design. I am beyond confused why they would design it this way. I have 2 return heads and both of them have sponges for debris and bubbles. they get dirty in a week. the one closer to the water just dumping in is way dirtier faster but I cannot imagine this is by design. again, I have no real experience so im learning this style but is this correct? I ask because the main reason im worried about the little bit of overflow is this is bypassing any filtration. but it might not matter if the other half of the weir is just dumping water into it with no filter.... either this was an oversight, im doing something wrong, or my understanding is wrong. if anyone can shed some light on this I would GREATLY appreciate it! thank you!
 
I'm not familiar with this particular tank and I've never owned a AIO. Plus, being a very visual person, I'm really struggling to understand your description of the issue. Could you maybe post some pictures? Or, better, upload and video to YouTube and post a link here?
 
sure, here is a photo of the overflow. I dont have any way to post the video I sent to Red Sea to identify the issue and the site wont let me upload a video only link one. I dont have any of the accounts it allows. thank you!
Screenshot 2026-01-29 at 10.06.09 AM.png
 
Maybe I'm being dense (entirely possible) but, I'm still not able to picture what is happening.
 
no worries, so the weir is on the right side, the sump area is on the left. the water you see after the fingers of the weir is sitting in a small box. that box plumbs into the nano mat. whats happening is the box is overflowing and the water is spilling out the back, bypassing the nano mat filter. since I know what im looking at it makes more sense, but what you see on the back side of the box that is shiny is the actual water overflowing. ill try and mark it up a bit. maybe not the most elegant but the second one has 2 parallel lines. between them is the overflow. it usually runs the whole length of the box. its like a waterfall really. ill see if I can find some place to put a video later tonight. that will easily explain what im struggling to. ill also attach red sea's sump photo. where their filter sock is, I have a nano mat. otherwise its the same.
 

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Great pictures. I think I understand what you're describing now. To make sure I am, the water should NOT be going where you state, "Flowing over the back" but, instead, should be going straight down (green arrow I inserted) and coming out the bottom to the left of the divider. Is that correct?
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Sounds to me like either 1. something is restricting flow underneath the "divider." or 2. your return pumps are too strong. Those two items would be the first thing I'd check.

I'm spitballing here of course but, trying to help you figure this out.
 
thank you, that is what it was. I found on the official Red Sea forum others with this issue. it is a combo of the nanomat not keeping up and the return pumps too strong. I just assumed all being Red Sea it would work. apparently thats true IF you dont have a wave maker and are running a pretty clean tank. the filter restricting and way too high flow of the return pumps plus wave maker is causing it. I really appreciate your advice. thank you!
 
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