I'm sure this topic has been covered multiple times before and I've been reading all I can on the subject, but I'd like to address my specific concerns here.
I recently purchased a used 120g with dual overflows.
Photos: https://drive.google.com/open?id=0B3-9-sy4j_dmdnBzRXFyci1EMTQ
Purchased is a strong word as I won the tank but have yet to pay as I have concerns.
I've been running a 60g with a single overflow for years so I understand all the concepts on the single overflow. But the dual overflow has me concerned, mainly with the plumbing. I've read with dual overflows you will never achieve balance, which makes sense as each return pump, even if identical, will perform slightly different. I also know each overflow will clog with algae and other fine particles at different rates, even further altering the intake and output of each overflow.
There's also the issue of configuration in the sump, as typically my experience has my sump setup as: overflow down to sock, then to skimmer, then to GFO/carbon reactor, finally to return pump. In a dual overflow I can plumb one to go straight down and then plumb the other overflow across the sump. But this will unbalance that overflow even more given the further path it needs to travel down the pipe. Also, one overflow's return pump will have more head pressure and further to travel back to the tank than the other. I can compensate with running a larger pump, but again even more unbalance.
Using a T-fitting to merge the 2 overflows into 1 sounds like a failure, as both pipes will then be forced to converge into a single pipe, causing a backup. I could rip one overflow out and plug the holes, but I dont know if a single overflow can handle it all on its own. I'm not going to increase the hole size in the weirs or drill more holes or make bigger holes, just not something I'm willing to do. I would rather just get a different tank.
The only option I've read that kind of makes it sound like this could work would be to have one overflow converted to a herbie, and leave the other as a durso.
(This isn't my plan, I read it on another forum addressing the topic and it made some sense)
1). Leave the right drain alone as a durso pipe and plump it into your sump.
2). Replace the left durso pipe with PVC maybe half the height so it's under water.
3). Setup the drain as a herbie with a gate valve on it and plumb it into your sump.
4). Close the gate valve all the way.
5). Turn on your return pump to make sure it does not overflow with one drain. It should make all kinds of nasty sucks, flushing sounds. But it should not overflow the tank. you may have to turn down the return pump with a bypass.
6). Open the gate valve slowly until a perfect siphon is reached on the herbie drain ensuring that it is always under water.
7). A little flow should be seen in the durso pipe side.
But again this is new to me and I'm not sure it will work.
I wanted to ask this community for any help they could provide as I know this isn't a new problem. I'm not all that handy, so if the plan is much more complex than the one I pasted above then I probably dont feel confident I can do it. I'd rather just find another tank with a larger, single overflow.
I recently purchased a used 120g with dual overflows.
Photos: https://drive.google.com/open?id=0B3-9-sy4j_dmdnBzRXFyci1EMTQ
Purchased is a strong word as I won the tank but have yet to pay as I have concerns.
I've been running a 60g with a single overflow for years so I understand all the concepts on the single overflow. But the dual overflow has me concerned, mainly with the plumbing. I've read with dual overflows you will never achieve balance, which makes sense as each return pump, even if identical, will perform slightly different. I also know each overflow will clog with algae and other fine particles at different rates, even further altering the intake and output of each overflow.
There's also the issue of configuration in the sump, as typically my experience has my sump setup as: overflow down to sock, then to skimmer, then to GFO/carbon reactor, finally to return pump. In a dual overflow I can plumb one to go straight down and then plumb the other overflow across the sump. But this will unbalance that overflow even more given the further path it needs to travel down the pipe. Also, one overflow's return pump will have more head pressure and further to travel back to the tank than the other. I can compensate with running a larger pump, but again even more unbalance.
Using a T-fitting to merge the 2 overflows into 1 sounds like a failure, as both pipes will then be forced to converge into a single pipe, causing a backup. I could rip one overflow out and plug the holes, but I dont know if a single overflow can handle it all on its own. I'm not going to increase the hole size in the weirs or drill more holes or make bigger holes, just not something I'm willing to do. I would rather just get a different tank.
The only option I've read that kind of makes it sound like this could work would be to have one overflow converted to a herbie, and leave the other as a durso.
(This isn't my plan, I read it on another forum addressing the topic and it made some sense)
1). Leave the right drain alone as a durso pipe and plump it into your sump.
2). Replace the left durso pipe with PVC maybe half the height so it's under water.
3). Setup the drain as a herbie with a gate valve on it and plumb it into your sump.
4). Close the gate valve all the way.
5). Turn on your return pump to make sure it does not overflow with one drain. It should make all kinds of nasty sucks, flushing sounds. But it should not overflow the tank. you may have to turn down the return pump with a bypass.
6). Open the gate valve slowly until a perfect siphon is reached on the herbie drain ensuring that it is always under water.
7). A little flow should be seen in the durso pipe side.
But again this is new to me and I'm not sure it will work.
I wanted to ask this community for any help they could provide as I know this isn't a new problem. I'm not all that handy, so if the plan is much more complex than the one I pasted above then I probably dont feel confident I can do it. I'd rather just find another tank with a larger, single overflow.
I used both returns and both drains. I should point out that I run my system off a manifold. I control the amount of flow to my skimmer, UV, and drains with the turn of the handle on a ball valve. What helped me decide how I wanted to plumb my tank was searching "plumbing dual drain aquariums" on Google. Look at some of the pictures there and I think that you will get an idea of how to make yours work for you. Your thinking is good in that the more mechanical stuff you put in your sump/DT, the more heat you will have to deal with.
