Koi pond 2010,

One of the things that you didn't say is the size of the pipe going from bottom drain to SC. Since the pump is in the SC it should not have any problem pumping 2400 gph to the filter as long as the pipe going between the two is the correct size. The two 2" return lines won't have a problem as long as any air bubbles in these pipes can bleed off. Now the question is what size pipe needs to be to get enough water to the SC. To figure this correctly we need to know the length of pipe from the drain to the SC and all the fittings used. If the piping from the drain to the SC is 10 ft including fitting a 2" pipe will have just under a 4" drop in the water level in the SC to get 2400 gph to the SC. A 3" pipe in the same example the SC would have just over a .5" drop. So with the right piping everything will work.
Mike

Hi Mike,

Thanks for the feedback. Yes the bottom drain to the SC is 3" all the way with hopefully two 90 degree bend.

You also mentioned about air bubble trapped on the return line. I had this problem in the past. That's why I put in two 2" pipe. Is it possible to design a system free of air bubble trap in a return gravity fed system?

Koi_pong_2010

Koi pond 2010,
Okay your two 90 degree elbows equal 16 ft of 3" pipe. I assume that you may use a bulkhead fitting and each of those will add to the length of the pipe. Then all the fittings connecting to the bulkhead will add to the pipe length. Also the fact that water is going from a large area to a pipe and then back to a larger volume adds to the length of the pipe. You could easily get to 30 or 40 ft of 3" pipe. At 30 ft the SC will drop about 2 inches at 2400 gph and at 40 ft it will drop about 2.5 inches.
Now looking at the possible air bubble entrapment. Air bubbles are trapped either at elbows or in horizontal runs of pipe that have a high point in the center of the run. The way to fix these problems is the elbows coming out of the filter are replaced with a tee with the through branch of the tee being vertical. The highest end of this tee is left open to the air so that any air inside the pipe can get out. Any elbow that does not turn the water to a downward direction is not problem. The other place you can have a problem with an elbow is where it empties into the pond. If the elbow is on the pond side of the edge of the liner then a small hole can be drilled in the top of the bend of the elbow and the air will bleed off. If water comes out this hole it will flow into the pond. If it is not in this position then it becomes more complicated but can be done. On the tee installation a small piece of pipe may have to be put in the open end to keep the possibility of water coming out.
Mike

Mike,

Thanks for the feedback. It was very informative and I will Incorporate some of your ideas ( adding a Tee on the return line ) into my design. I will keep you posted and hopefully a picture in a 2-3 months.

koi_pond_2010.

Hi Mike or anyone

My plan has changed a little. The length of plumbing(3")/vacuum drain(3") from the pond to SC is now 26' and has 3 elbow total. My SC is now 110gal ( instead of 45gal ). The submerged pump in my SC is still 2400gph (1" diameter outlet). This pump will have to pump water from SC into my main filter which is elevated by 1.5 feet and the flexible PVC is about 4' long.So my question is how much water level dropped will I see in my SC?

Thanks

Koi pond 2010,

The 26 ft and 3 elbows are going to give you the same amount as 50 ft of pipe. This is going to give you just over 2.8 inches of drop at 2400 gph. If you plan on running 1" pipe to your main filter you won't get 2400 from the pump even with 4 ft of pipe. Also I do not know how many ft of pipe to add for the drain connecting to the pipe or the pipe going into the settling chamber. I know you will have more drop then what I just said but how much I can't say without more information. Are there any more fittings. What drain are you using? How are connecting to the SC? I am guessing that the total length of pipe including fittings is going to be closer to 60 or 70 ft.
Mike

Hi Mike,

Thanks for the quick response. 26 ft and 3 elbow is from one side of the liner ( bulkhead fitting) to the final outlet(another bulkhead fitting)in the SC. I do need to add about 3ft of 3" pipe inside the pond. This extension goes all the way to the bottom. There's no plumbing inside the SC. My bottom drain is not a true bottom drain. It's more like a vacuum drain. It goes through the liner at mid point ( 1.5 ft below ground level ) and continue all the way down to the bottom of the pond. I have a partial above ground pond. It's 1.5ft above ground and 3ft below. And my SC is more like a pre-filter ( mechanical ) than anything else.

So bottom line is from end to end is 29ft, 3" pipe and 3 elbow.

By the way, what do you use to tighten your 3" bulkhead fitting? The outside diameter ring is 5.5".

Thank for the feedback. I really appreciated it.

Hi Koi Pond,

Let me go over how to calculate the length of pipe including friction. Going from inside the pond to the SC. First is the reduction of the water flow from the bottom drain into the pipe. That is the same as 2 ft of the larger diameter and 4 ft of the smaller. Then we have the connection from the drain to the pipe. Since I don't know the drain type I am going to assume that it is a simple glue joint which is 3 ft of pipe. Then we have 3 ft of pipe in the pond. A male adapter going into the bulkhead and male adapter coming out. Each male adapter is 6.5 ft and bulkhead is 4 ft. Then you have 26 ft of pipe and 3 elbows each are 8 ft of pipe. Another male adapter and bulkhead fitting. Then we have the water expanding in a larger container which is the same as 2 ft of smaller pipe and 4 ft of larger diameter. Since the pond and the SC are large enough that ft in these diameters would not change the end result so we will not count those. Now I am going to list the numbers in the order that they appear in the pond to the SC. 4+3+3+6.5+4+6.5+26+8+8+8+6.5+4+2=89.5 ft of 3" pipe. If you are actually removing 2400 gph from the SC the water drop will be about 5". If you change to 4" the drop would about 1.75 inches.

I use a 20" pair of channel locks to tighten 3" bulkhead fittings.

Mike

Thanks for the feedback.
Sounds like changing to 4" pipe is a better option. Instead of one 4" pipe system, if I have two 2" pipe system ( meaning two independent 2" bottom drain feeding the same SC) would it do the same job as one 4" pipe system?

Thanks.

Two 2" systems is a little less then one 3" system. The other problem is that each system is only going to have 1200 gph per drain which is not much.
Mike

It's a new and yet cycling pond. I introduced 4 Koi fish to start my cycle.
My system is made of mechanical & biological Filters, UV and 02 air bubblers.
My 4 Kois lived for about 1 month and a half. They were doing quite fine and swimming around nicely. suddenly, one morning, I wake up to find out my 4 koi fishes dead! They had no white spot; their skin naturally slimy; but all four died overnight for no apparent reason. pH8, Ammonia 0, Nitrite 0, Nitate 0. No tester for Chlorine!
I am trying to find the reason of their sudden death. Could it be the use of swimming pool vacuum cleaner to cleam pond (polluted with pool's chlorine)? Or could it be the lack of oxygen? I don't hear/see the air bubblers operating while filtration system is ON. Does the A/bubbler must be switched ON continuously when the filter is running? Or does it run by intermittence?
Please, I need help 'cause I'm afraid to add any more fish, unless i can understand and resolve the problem...Anybody has an idea??