Sump Flow Question

  1. locoyo386 Well Known Member Member

    Hi all,
    I have a question with regards to water flow in the sump. Well let me start by saying that I have lots of tanks, but none are filtered with sumps even my big tank. I just upgraded one of my 55's to a 120 RR tank. So far I regret doing so, cause I can't seem to get rid of the micro bubble and can't seem to get really good mechanichal filtration without restricting my pump outflow drastically (which lowers my water level in the pump chamber). I have researched quite a bit on sumps (but still very naive when it comes to designing them) but I think that I have designed my DIY sump wrong, at least when it comes to the flow in the sump. I design the sump as a channel flow that starts at one and and circles around to the same end but opposite corner. The overflow drops at the back left corner and my pumps sits on the front left corner. I have a standard 20 (24"L x 16"H x 12"D) gallon tank (it was the only one that would fit under the stand) for the sump. The question that I have is complicated to answear as it might depend on the way the sump was designed, but I woul like to ask it anyways. What should my flowrate be in the sump this size? and hope to prevent the microbbubles and water level issues that I have once I place mechanichal filtration media. If anyone has thoughts on this, I would greatly appreciate it if you shared them with me.

  2. Shaina Well Known Member Member

    Flowrate depends on how much and what kind of filtermedia you have as it is really a function of how much surface area you are running the water over in a given amount of time. The standard "cannister filter" flow rate is usually given to be about the volume of your tank 5x/hour, but cannisters are usually filled with filter media designed to have extraordinary amounts of surface area/volume. They can also pack that media tighter than we sump-users can because they have more water pressure to force the water through.

    Microbubbles are usually dissipated using relatively tightly spaced baffles...from your description I'm not sure that you are using baffles at all so the entrained water lightly doesn't have time to dissipate.

    Water level issues...if the the sump is able to sustain the water flow you want without media, then chances are your media is not permeable enough for sump use, which is a common mistake (and one I've made). As nice as it is to use the fancy pads that scrub microparticles from the water, the unfortunate thing is that without the additional water pressure sustained in a cannister, the only way to use them in a sump is to have a sufficiently low flowrate to allow the water to pass through, and/or a large section of the cloth to give more surface area for water to pass through.

    Kinda babbly because I'm in a hurry but I hope this helps a bit.

  3. locoyo386 Well Known Member Member

    If I understand the canister filters correctly, they act more like a closed loop than an open one, right? The sump is open loop, right? If so than the ristrictions in the canister filter does not really matter as the water being succked out of the tank is what comes out of the naister filter and back into the tank. Thus the flow rate does not affect anything other than it will move less water.

    I do have 3-sets of baffles. The first one is a single one that is right after the inlet of the sump (the water leaving the DT and coming into the sump). This baffle is about 1" in width. The second set is more like chambers that allow for media to be placed and they wrap the tank at the other end (they make a 180 turn). On the back right corner is one of the baffles (chaimber) that is 3"x7" and feeds into another baffle (chaimber) that is 3"x5". The third set is just before the return pump and there are 2 baffles that are again around 1" in width. The water flow through the sump is channel froma 7" wide to a 5" channel that are of different heights as the flow goes thought the sump. The highest level is around 11" at the inlet and in the first main chamber of the sump (where I have sand and live rock, similar to how wet/dry sumps have bio-balls) than it drops to 10" into the second set of baffle and second chamber (refugium for later, with DSB). Than there is the 3rd set of baffles that consists of two 1" chambers that allow for bubble difusion.

    Yeah, and that's part of the problem that I have. When I place the pads the flow is restricted so much that the level in the return pumps goes so low that when the water evaporates it might allow for the pump to run dry. I have tried placing it in different areas but at the end I get the same result. I am thinking that I might have to take the sump out and make a custom one (that is bigger and allow for more volume in the return chamber) cause I would not want to go to a smaller pump, unless I can figure out how much flow I can run through the sumop with no problems. I have posted this question, but seems it might have tocome to trial and error to figure that one out. Either way thanks for your imput.

  4. pepetj Well Known Member Member

    Keep in mind that FW wet/dry and SW sump although similar in construction work differently. The FW sump usually operates with a smaller volume of water than a SW sump/fuge.

    I figure you need to build a bubble trap (which is achieved easily with three baffles). Please google info on this simple idea. An easy way of looking at this is that the return pump rate must balance out with the intake flow, otherwise you'll sump will work towards either drying out or flooding. The maximum flow on the intake will determine the maximum flow rate of the return pump (compensating the head loss).

    If your only problem is microbubbles, then you already achieved that balance. I place the return pump at one extreme of the tank, then I used three glass (acrylic works) sheets that I kept around 1" apart from each other, with the middle one leaving one to one-half inch space towards the bottom while the ones at the sides are attached to the bottom work nicely well. I have no bubbles in my DIY sump.

    Santo Domingo

  5. locoyo386 Well Known Member Member

    Not sure what you mean by differently. But all mechanichal filters (canister, hang on the back, sumpa, wet/dry, trickle and many more) work the same way. You pass a stream of water through the media ro filter particles from the water column. The media will determine the final flow rate of the filter. Which is in part the problem I am having. The filter pad is not pourus enough to let enough water through without draining my return chamber too much.

    [/QUOTE]I figure you need to build a bubble trap (which is achieved easily with three baffles). Please google info on this simple idea[/QUOTE]

    As stated above I have 3 sets of baffles to trap bubbles, but the flow rate going to trough the sump is too strong. The flow becomes turbulant and it creates additional bubbles. Which leads to the quetion at hand, how can I figure out what the maimum flowrate that a sump can handle? I am thinking it's going to have to be a trial and error type of scenario to figure that out, or look more into fluid mechanics.

    That is correct now, what determines the maximum flowrate through the sump. I know it has to be a function of retrictions, like filter pads, o-rings, foam stars, ceramic cylinders, carbon filled socks or and any other media that can be used. It also has to do with the size of the spacings between baffles and any other opening that the water is flowing through. I feel that is giong to be more complicated than just using some other type of mechanichal filtration.

    If you buy a sump pre-made by a manufacturer. Thye will rate the sump filter for a specific size tank just like they do for hang on the back filters. If you wanted to find out what the maximum flowrate through the sump (pre-made), how would you go about figuring that out (I do belive that is independent of the tank, and more dependent on the restrictions as mentioned above)?
  6. locoyo386 Well Known Member Member

    Thankyuo all for the info. and help. I am finding out that it's too much of a headache (trial and error) and costly to make my current sump work right. Thus I am going back to the drawing board and rethink my whole mechanichal filtration sytem. Thanks for the help.