Help with connecting 2 tanks?

[scrapman]

I plan to connect a 90 gal (already established) with a 20 gal high... Both tanks will be side by side at approx the same level.... I have 2 Fluval 405 on the 90 gal.... I want to draw water from the 90 gal to the 20 gal and return it to the bigger tank.... all this without risk of flood if a pump or an overflow box fail!
I've looked at all the sump threads.... usually a sump stands hidden below the DT.... My case is different... I have no experience in this type of plumbing.... I'am willing to learn!
Any suggestion?
Thanks

 

[reefforbrains]

Is there a third tank or Sump?
If theres a sump then just run it the same way with a T on the return to give the little 20 a little something.
For the record. Joining water volumes typically brings bad news as everything being connected is a nice boon for stability of the system when things are going good.
Downside is when something goes bad it can make a catostropic system problem wiping both tanks out.
Why would you want to merge them in the first place if I might ask?

 

[scrapman]

Thanks ReefForBrains
No sump in my system... my 90 gal is squeezed between 2 rooms (perfect setting, seen from both sides, like having 2 tanks).... I just have a perfect spot to ad a 20 gal high next to it.
I understand the logic of if something goes bad, the 2 tanks are doomed....
I do not understand the plumbing involved to connect the 2 tanks which will be on the same level next to each other....
Could you pls walk me through the process for a foolproof setup (no flood, no leak)...
Thanks

 

[hurt]

They can't be even or they won't drain into one or the other(at least the top of the tanks). One must be higher than the other so it can "overflow" into the other with the help of gravity. It sounds to me as if you want water to go from your 90 and drain to the 20, then get pumped back. In such case, the top of the 90g must be higher than the top of the 20g. I'm not certain the dimensions on a 20H but I would think it is not as tall as a 90 is. If such is the case you could have each tank on the same height stand(meaning the bottom of each tank is flush). Your return pump will be in the 20H returning back to you 90. As such your water level in your 90 will never change. You will see fluctuations from evaportation in your 20H.
This is where you run into the problem, accounting for the excess drainage into the overflow when the power goes out and the return pump stops. In this event water in your 90 will drain down to the top of the overflow intake, which usually means at least an inch of water from your DT will enter your 20g. For a 90g(without the exact dimensions of your tank) I would say it is safe to say at least another 5-6 gallons will drain back your 20 when the power goes out. Which means you can't have a normal operating water level in the 20H more than 15g at most, which means you can only fill it up roughly 3/4 of the way.
I'm not sure if you want that or not, but another option would be to add another 20g, but this tank would be at the lowest height in your system and it would house your return pump sending water back to your 90g. As such you will need an overflow for your 90g to get the water to your 20H. I would take the 20H to a glass shop and have them drill a 1 inch bulkhead in it for a drain, so it can then send water to the 20g at the lowest point in your system. This way your 20H can be filled with water, as the 20g below the 20H will now be the tank to take in excess water when the power goes out. Hope that wasn't too confusing...
This is a thread in which I discussed something similiar which might help.
link
If you decide to do it, I can help you out with specs a bit more. I have three tanks plumbed into my sytem-DT, fuge, sump and it is pretty much the same diagram as the one posted below

 

[scrapman]

Thanks a lot HURT
I understand better now...
I cannot host a sump..... my stand is open.... no equipment under the DT.... 2 pumps on the side against a wall.... The 20 gal high will be positioned on a matching stand against that wall, touching the corner of the 90, above the pumps...
Now, to avoid the large drainage that you mention, it seems to me that the top of the 20 gal should be below but very close to the 90.... (let say that there is a 2 inch difference between the two water levels)... There will still be a siphon from the 90 to the 20 but, in case of a power outage, the drainage will be minimized...
Am I correct?
Thinking about it.... I'am not... 2 in of the 90 gal is what you have said...
Having the 20 gal at 3/4 of capacity sucks!
What about an overflow which stops when the power is off???
Thanks

 

[andy51632]

I would not connect them man. If I were you I would go ahead and put the 20 next to the 90 (separate). It should not set you back much to get equiptment for the 20. It would be a great QT tank. You could use the water from the 90gal water change to change the 20gallons water no extra cost there. You could also make it a fuge but you would not be able to have anything in it but lr.

 

[scsinet]

The simplest and most reliable way to do this is to drill both tanks on the side near the bottom, and link them that way.
As stated, the pros are reliability and simplicity.
The cons are that you need to drill the tanks -- which takes skill and special tools (though easily attainable), and that the tanks would need to be empty --, and that the TOP of both tanks needs to be on the same level, not the bottom.
Another thought... if your stand is open, can you place the smaller tank below the stand and have it down there... a "sump" per se can also be a "display tank." To do this, you'd put an overflow on the top tank draining down into the bottom. Then have the Fluval pull from the bottom tank and return to the top.

 

[scrapman]

Thanks SCSInet
drilling is out of question now....
The idea of the 20 gal High below the 90 is appealing... What is there is a power failure..... the 90 gal drains into the 20?.... how to limit/stop the siphon??

 

[hurt]

Originally Posted by scrapman
Now, to avoid the large drainage that you mention, it seems to me that the top of the 20 gal should be below but very close to the 90.... (let say that there is a 2 inch difference between the two water levels)... There will still be a siphon from the 90 to the 20 but, in case of a power outage, the drainage will be minimized...
Am I correct?
Thanks
The height of the 20g relative to the height of the 90g is irrelevant as far as stopping the drainage in the event of the power outage. The overflow will drain down to the top of it's intake(the teeth on the inside box) regardless. It will also drain down to the top of your return line plumbed back to your display tank. That's is why many return lines are at the very top of DT. You could put the return line lower in your DT and just drill a small whole in the top of the return line just under the top of the water level in your DT, this lets air in to break the siphon so it won't drain any more on the return line.
The main point however that I was really trying to make is that the bottom of your overflow(on the outside of your DT), this MUST be higher than the top of your 20g if you want it to drain.

 

[hurt]

Originally Posted by scrapman
The idea of the 20 gal High below the 90 is appealing... What is there is a power failure..... the 90 gal drains into the 20?.... how to limit/stop the siphon??

You can't stop it, it will drain down at least 1/2 an inch in your DT to the bottom of the teeth on your overflow. To figure out exactly how many extra gallons your 90DT will throw into your 20g you just take the L*W*D(where D is always 1) of your tank and divide that number by 231. In this formula normally you use L*W*D/231 to convert to gallons in a given space. The D is 1 in the overflow formula to be safe. That is your depth of the tank water(1 inch at most) that will drain into your sump when the power goes out. This figure is more than generous, and you probably could use .75 for D and still be safe.
I am assuming your 90DT is 48 inches long and 18 inches wide. In such case (48*18)/231 is ~4 gallons. And that figure is being very safe. So your 20g can't ever have more than 16g in it to compensate when the power goes out.

 

[big400g]

Not to hijack, I am planning to have my 300 and 92 as part of one large system. Plumbing out of the overflows into the sump and from the sump to both tanks through a T. My thought was that it would increase stability and make things better. After reading this thread I am starting to wonder if that was a good idea. I am not going to have water go out of one tank into the other directly because both tanks will have the same water height.
Any thoughts?