display tank water level

I have recently got my new 250G up and running. I have dual 1.5" overflows that go into a 2" pipe to the sump. I had a sequence dart as the return pump but the water level was too low. So i upgraded the pump to a sequence barracuda. I now have to throttle this pump back a little bit to prevent overflow. The problem is that the water level does not remain constant it fluctates by about 3/4". Im worried that there is not a very big safety margin, in the overflow. ie if the drain line gets a small blockage then the tank will quickly overflow. I have thought about adding air valves to the vent holes in the top of the dorso's which will speed up the overflow, but will not increase the error margin. Anybody have any ideas?
thanks

 

The overflow boxes dictate the water level of the tank .. You did not just shove a few pipes into the tank and trying to use them as a tall open site drain are you ? Like a building floor drain on a pole ?

 

no. This tank was built by the previous "Aquariums for you" it has dual overflow boxes (im guessing to be about 6X12 each). any suggestions

 

If the water level in the overflow box is fluctuating it sounds like the drain pipe is trying to pull a straight syphon and then it loses it. You said you were using durso drain pipes. You can make the air inlet in the top of the cap a little bit bigger and by a little bit I mean a little at a time. if you over do it you'll have to try and change the top cap or epoxy it back closed a re drill it. Without enough air flow the durso's won't keep draining and they'll try to syphon the water out...

If the water level in the main tank outside the overlfow boxes is fluctuating I'm at a loss...

 

If its the main tank fluctuating out side the overflows then there is a leak in the box some where if as Kogle said then you have a siphon issue how high does the level behind the overflow run ? I raise my drains so that the water passing through the weirs only falls about 2 inches before it mixes with the water level behind the overflow .. Or you may not have enough main pump or there is a blockage from the sump back to the tank..

 

Thats what has always confused me. In my old 90G the water level inside the overflow was about 1 inch below the tank level. In this tank they are equal. There does not appear to be any leaks as i have had the tank full of water and the overflows did not leak any water in to them. Kogle: the drain is not syphoning the water as the level inside the overflow is ALWAYS the same as the tank. YES, it is the water level in the tank that is fluctuating, a couple of times the water level in the tank has gotten to a scary point (of overflowing ) and so i have placed a finger over the air hole to speed up the draining. till i get out to close the ball valve on the return a little. Tangster: the main pump is a throttled back barracuda it should be plenty of pump. I really dont like having this low margin for error. anyone?

 

Is your overflow adjustable? how big is your sump? maybe you need to down size the pump!
or there might be too many elbows in you drain pipes, have you checked for bioballs or something inside your drain pipes that could of cause an obstruction?

 

Sounds like your return pump is pushing too much water. Also the stand pipe in the overflow box is too high.

J

 

That's what I was going to say on the standpipe. I'm glad I made mine adjustable....

 

That makes sense, i will try lowering the standpipes, they are not adjustbale but the joints are only taped. Jason, I had originally had a sequence dart as the return and the water level in the tank was too low. Aquariums for you told me it was because the return pump was too small, hence the upgrade to the barracuda. thank you all for your input. Ill let you know how it works with the adjustments.