Anaerobic conditions in internal overflows

[Humu Humu]

I have to share this incident which occurred last evening. I have a 125 Oceanic tank with twin internal overflows. They have two holes drilled at the bottom, where you put your bulkheads and run a standpipe, with a Durso to the operating level in the overflow. Very common setup.

Yesterday, I was fiddling around in the overflow, pulling out some algae that had accumulated at the surface and around the Durso. No big deal, I've done this hundreds of times. We then went out to dinner.

When we returned, the place had the most horrific stink! It smelled like something died in the apartment. We surmised that the odor was coming from the tank. I was confused, as the tank has no foul odor whatsoever. Looking under the tank I noticed that there was a slight drip beneath one of the bulkheads. I must have jostled the standpipe a bit too much when I was removing the algae a few hours ago. Still, no explanation for the rancid smell. I put a bucket under the drip and resolved to fix it the next day.

Today, being that day, I looked beneath the bulkhead and noticed the lock ring was loose, therefore allowing the slight drip. I tightened up the lock ring and the drip stopped. Again, no big deal, done this a few times as well. The smell immediately went away.

This got me thinking....The drip was coming from water that sits at the bottom of the overflow, deep down, where it gets little to no circulation, not like the surface of the overflow, where water movement is evident. Who knows whats at the base of these overflows? My tank is over one year old. Apparently, enough has settled in the overflow to become rancid at the bottom with anaerobic conditions present. The problem, is there is really no good way to clean this out, short of stuffing a siphon hose in there and trying to siphon any gunk that may have accumulated.

My next tank will have an external coast to coast, or something similar, shallow enough to allow me to keep it clean. I consider this a design flaw in the internal overflows.

 

[Jeremy05]

Just cleaned that area out on my 75 gal and like you said I've had tank for a year and never cleaned. I had to stick a hose back there and it was the most disgusting **** I've ever seen/smelt. It turned 35 gal of water pitch black. Also make sure you do the same in sump/refugium for any excess build up. GL

 

[Humu Humu]

Jeremy,

Good to know. I'll hit it with a siphon this weekend. I never liked those internal overflows. Take up too much room and now this.

Thanks,

Dave

 

[Decadence]

I clean it out every couple of months. It takes a lot of accumulation in order for it to get to the point where hydrogen sulfide is being created. Syphoning it is pretty simple and you can check your progress by looking up through the bottom of the tank to see where you still have to get. I can't even begin to fathom how bad it is between the two pieces of plastic in that very narrow region. I have to say that like you, I am not a fan of reef ready overflows for this reason.

 

[ca1ore]

Certainly a lower flow through the overflows can result in buildup on the bottom. You might want to consider increasing the flow through your sump, or drop a small power-head into each overflow, put them on a timer that runs them an hour each day.

 

[Humu Humu]

I'll hit them this weekend with a siphon and hope for the best. I was always hesitant to go in there because you can bump the riser pipes and end up with a leaky bulkhead that is not always a quick fix. I'll just have to be really careful with the siphon hose.

 

[Psyops]

Certainly a lower flow through the overflows can result in buildup on the bottom. You might want to consider increasing the flow through your sump, or drop a small power-head into each overflow, put them on a timer that runs them an hour each day.

That's a pretty good idea ca1ore.


I found out this issue when my flame wrasse jumped back there. I got him out and found out what crap was down there. I honestly forgot to clean that area. I did use a 1 inch ID line and suctioned the water out. And yes, it was discusting.

 

[mr.maroonsalty]

I run a syphon drain straight through only the bulkhead; no build up of detritus here for me. In between the two layers that the box has may be a different thing though.

 

[dkeller_nc]

Well, this is one disadvantage to Durso/Herbie overflow standpipes over the old-school method that has a drain fitted with a strainer at the bottom of the overflow that I've never considered. Certainly makes sense though - a 15" tall water column in an overflow could certainly build up a detritus layer that could go anoxic/anaerobic.

Regarding putting a circulation pump in the overflow to prevent detritus from settling, folks reading this thread might consider one of the Sicce mouse pumps. They use 6.2 watts and have a relatively broad, low velocity flow for their size.

Here's another idea - add a small, 1/4" piece of RO tubing to your return pump's piping, and hold it in place at the bottom of the overflow with a magnetic tubing holder. I would think that would be just enough flow directed against the bottom glass to prevent detritus from settling there. Although a larger overflow might require something bigger, like 3/8" or even 1/2" hard piping.

Very interesting, and something I've never thought of b/c my 50 gallon cube is my first tank with a "modern" overflow set-up. Thanks for posting this!

 

[Humu Humu]

Mr. Maroonsalty,

You run a straight siphon drain from the overflow bulkhead out, with no standpipe? How do you control it, with a ball or gate valve? I'm thinking of a Bean Animal style setup with one siphon, flush with the bulkhead, and one durso overflow. Choke down the siphon to build up the head in the overflow to the durso level. This way, you could drain the overflow at any time for maintenance by simply opening up the siphon valve.

 

[Humu Humu]

I just want everyone to know, I vacuumed it all out. It wasn't too bad. 3 five gallon buckets of stuff. I even removed the overflow tubes and let the water just flow down the bulkhead opening. On one of them, I didn't even put the riser back, as is was fairly silent. Good to know as maybe a quarterly maintenance item.

 

[mr.maroonsalty]

I have duel overflows tied together. The two 1" bulkheads connect into 1 1/2" pipe (more than twice the volume of 1") I control the syphon with a 1 1/2 ball valve, however, I also have a 1" gate valve that works as a great fine tuner; a simple wye is all thats needed, and cost wise a 1 1/2" bv + 1" gv ~< $ 1 1/2" gv. I use two 1 1/2" PVC standpipes for back up; just the pipe without any fittings on top. The water needs to be kept fairly high or there is a water fall sound from the water going over the bulkhead which I cut down half way through the slots for a weir. I can run it either Bean or Herbie style depending on what pump I want to use (or impeller).

 

[G4546]

Certainly a lower flow through the overflows can result in buildup on the bottom. You might want to consider increasing the flow through your sump, or drop a small power-head into each overflow, put them on a timer that runs them an hour each day.

I thought this to be a pretty good idea myself

To the OP: I bet your system has really enjoyed the removal of 3, 5gallon buckets of mucky nastyness

 

[animalkingdom]

hmmm never had this problem...i guess i get a good cascade over the top that mixes everything well?? detritus accumulates very very slowly in mine if at all.