Standpipe flushing

[ldmk]

I just finished a week of struggling with setting up my tank and was happy that I had defeated the last leak yesterday. The tank seemed to be doing fine but all of a sudden today I discovered that the standpipes have started "flushing."

I am using two Durso standpipes (one in each overflow box) - using 1" bulkheads and 1" pipes (didn't do the 1.25" expansion suggested by Durso). The caps are drilled on the top. They were functioning quite well, but today they have stopped working like normal. Instead of just letting the water run out, the overflow box is now filling up with water almost to the point of running over and then the standpipes are flushing in one rapid motion - only to repeat the process over and over again.

I assume that there is reverse pressure building up in the sump - and I am wondering if there is anything I can do to fight that. Am I pretty much stuck with letting the water splash into the sump without being able to have the water enter below the water level in the sump? Right now I have a couple of pieces of PVC connected to the bulkheads that allows the water from the drains to enter the sump about three inches below the water level.

Also, why did the standpipes work fine for approximately 36 hours before starting this flushing problem? Does this have anything to do with the water in the sump evaporating? [There is less water in the system today than there was yesterday.] Can I deal with the problem of the standpipes flushing by making the hole on top of the cap (on the standpipe) smaller/bigger/etc?

Sorry for this whole host of questions, but I am at a complete loss as to why the plumbing in my tank is going haywire. Any suggestions would be most welcome.

Thanks.

K.M.

P.S. I'll try and post pictures of my setup as soon as I have everything (really) working

[mojoreef]

drill a larger hole

[Calvinc4s]

Yup what Mojo said.
You want to slowly ream the hole out till the level in
the prefilter box levels out. Also, Make sure your sump level is where you want it befor you adjust the air hole.

Does this have anything to do with the water in the sump evaporating?

YES

[ldmk]

Thanks Mojoreef and Calvinc4s.

Just out of curiosity, why does the water in the sump evaporating cause the standpipes to start flushing? I'd would think it would decrease the back pressure in the sump and help the standpipes drain even more efficiently. Not questioning your response, just trying to learn some more

Thanks again.

K.M.

[Calvinc4s]

They drain faster and don't allow the breather hole to keep up with the changed flow. That is just a guess,

[thefatman]

here are a couple thigns to try also.

put wo elbows on the end of the drain in the sump, creating a "u" at the bottom of your drain line in the sump, casuing the water to drain UP instead of down. i've heard this creates a much more constant back pressure.

instead of trying to find just the right size hole to drill in the end cap, drill a hole in the SIDE of the endcap, this way all you need to do is rotate the endcap to adjust the hole bigger or smaller.

richard has a pic of this on his site. that's what i did and it totally solved the flushing effect.

good luck