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Old 05-14-2022, 01:05 AM   #1
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Pump size

As expressed in a previous thread I'm running a new 20 gallon cube with under gravel filtration. I would also like to use the tank's built in three stage filtration but the included pump is not acceptable as it is just too strong for the tank. I mean what use is a pump rated at 264 gallons per hour in a 20 gallon tank? To me it seems that it would be overkill in a 100 gallon tank. I inherited a couple of black skirt tetras and they can't even swim against the resulting current.


I want to replace the pump but, as I've never used this type of filtration, sponge, carbon and ceramic, I'm not sure what I should go with for the new pump, main fish will be ropes (if I can ever find any) which tend to prefer slow moving water. I'm thinking that the combination of the under gravel and the three stage built in filtration should do quite well even with a low output pump for the built in. Simple matter to replace the pump as it is not anchored; just hangs from the output nozzle.

I'm thinking along the lines 15-20 gallons per hour. Am I in the ballpark?


I could just put a valve on the output of the current pump but restricting the flow on a pump generates heat which I don't want. I tried an in-line dimmer switch on the power cord but the pump motor must be capacitor driven as the dimmer does not lower the flow, it just makes it pulse. Actually I put the dimmer on an extension cord, not directly on the pump's power cord, as I didn't want to void the warranty.

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Old 05-14-2022, 03:48 AM   #2
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You typically want the water to have a turnover rate of 4 to 6 changes per hour. You will lose say 30 to 50% of the rated output of your filter/pump when you factor in all the sponge and media. Depends how much media is in the filtration. So on the face of it your 264gph isnt that excessive for a filter operating on its own.

However you have your UG filter, so you dont need both filters turning over that much water. How much water is the UG turning over?

I wouldnt be surprised if a pump turning over the small amount you are proposing didnt have enough power to pull water through the filtration when its got media in it. It certainly wouldnt create any effective filtration. Not enough flow rate to carry any detritus in the water into the filter or for the water to be properly oxygenated so that denitrifying bacteria can survive. As a minimum i would want the filtration pulling 2 or 3 water turnovers per hour or the filter just won't do anything and you may as well not have it on and just rely on the UG filter. Based on 30% to 50% loss of output i would look for a pump rated at around 100gph.
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Old 05-14-2022, 12:43 PM   #3
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Thanks for the info.


I really don't know how much water the under gravel is moving and don't know how to gauge.
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Old 05-14-2022, 09:37 PM   #4
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Just to add more info...


I may not be able to supply the water flow being supplied by the UG filtration but the Whisper air pump is rated for a 40 gallon tank and mine is just 20 gallons and the pump is running full power without restriction. I would think that the water flow should be decent. It is enough flow to slightly move the plastic plants a little. This DOES bring up another question which I would think to still be on topic... Big air bubbles or little bubbles? Personally I think any difference would be trivial as we would be talking about the volume of air moving water, not the size of the bubbles. If any advantage at all I'd have to guess that larger bubbles could produce a very minor difference as a fine air stone could slightly restrict the air flow. I'm currently running what I would call medium bubbles with the air going through a hollow plastic diffuser. Does my thinking seem reasonable?
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Old 05-15-2022, 12:20 AM   #5
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Sigh, I may owe an apology as to this whole thing.


I plugged back in the 264 GPH built in pump just to try a few things. The Black Skirt Tetras still seemed to show swimming distress but I very well may have just not understood what was really going on as I have zero experience with this type of filtration.


The output nozzle for the pump is a thin wide thing (sort of fan shaped). I changed it to where the thin part of the output was vertical instead of horizontal and paid close attention. I noticed that my pleco and Cory cat didn't seem at all bothered so I threw in some food and the tetras had no issue as to feeding. This was like an hour ago. What I took as swimming distress MAY have just been the tetras 'playing' in the current.



We shall see what happens as to the cloudiness in awhile but I think the main issue was my ignorance as to this type of filtration.


With the built in pump's output nozzle horizontal the fake plants would be pushed almost horizontal. Since I aligned the nozzle vertical the 'leaning' of the plants is much less.


Where I freaked out was the seeming swimming distress but I have no experience with tetras. It is quite possible that what I saw as swimming distress was just the tetras playing. Like I said I have no experience with this kind of filtration or tetras.


Hopefully the last question on this filtration but who knows as only time will tell. Would you recommend using the activated carbon bags for the built in filtration or to just leave out? I've never used carbon when I used to go strictly UG filtration but I don't know this filtration system.


Once again I want to express my appreciation for the help offered! Still must be proven but I suspect that the problem was not the hardware but, rather, my ignorance.
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Old 05-15-2022, 03:58 AM   #6
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Im just setting up a similar tank to yours. Like i said the flow rate of your built in filtration isnt all that excessive, but the output nozzles may create excessive turbulence depending on how they directed. Aim them at the surface and the water flow should quickly disperse and cause less issues for fish that dont like high flow rate.

Carbon removes organic compounds. Generally this means.

- Tannins which colour the water, for example from driftwood or leaf litter you may have in your aquascape.
- Phenols which causes odours.
- The active ingredients in medications are often organic, so you use carbon to remove medication after the treatment period.
- Carbon with remove chlorine and chloramine, but not quick enough to use an effective water treatment.

Going back to my earlier statement about aquarium product suppliers selling you stuff you dont need. The carbon is very much one of these. If you arent dealing with any of these issues you dont need carbon. Once your driftwood has stopped leeching tannins, you dont need to keep using it. A properly maintained aquarium doesnt produce excess odours.

One thing i see sometimes circulated is that carbon helps with your cycle. This is partially true. Ammonia, nitrite and nitrate arent organic so carbon wont help with these. However, some organic compounds that are present can break down to ammonia, so carbon can reduce the amount of ammonia present by removing the organic compound before it breaks down. But your cycle can easily establish sufficiently to remove this anyway, so while i will accept it can help, it isnt needed.

Carbon is expensive. It only lasts a couple of weeks before it needs replacing. The reason they include carbon with your filtration is so you will use it because you have it, and then buy more and keep using and buying more because you think you must need it or they wouldnt include it. Use it to deal with a specific issue, when that issue no longer exists stop using it. I always have a tub of carbon and some media bags should i need to use it. Im running a new tank with carbon at the moment until im sure the new driftwood has stopped leeching tannins and will then remove it.

Many people use carbon all the time, and say it keeps their water crystal clear. I would say their water would be clear regardless. But, using carbon doesnt hurt anything and if they are happy with the expense then go with it.
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Old 05-16-2022, 01:00 AM   #7
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I'm noticing something with the air pump for my under gravel filtration that bothers me a bit. my current 20 gallon cube is the first tank I've had in like 30 years and I'm using a Whisper 40 (rated for a 40 gallon tank) to drive the risers. There is no restriction to the air flow yet the pump puts out less air than what I would have experienced 30 years ago. Has Whisper gone down hill or is it just that under gravel filtration is now consider mostly obsolete so they no longer make air pumps as strong.


I also must admit that I just don't understand how this built in filtration system is supposed to work. I just don't understand how the thing is supposed to work with or without a carbon pack. Mayhaps it is just a bad setup but just as likely it is that I just don't understand how they work.


OK... The tank is a cube with an enclosed section in the back. The back section has three sections.
1) On the left is a section for sponges.
2) The middle section is for carbon and ceramic rings.
3) The right section contains the pump.


There are two holes in the back plate, between the actual tank and filtration chamber that are about 4 inches from the bottom of the tank. There is one hole on each side. There is also a slotted grid toward the top of the sponge section. The sponges pretty much fill their section and one of the inlet holes is in this section. The other hole is in the pump section. The center section is only about half full even if using both the ceramic and carbon.


I hope that is a decent enough of a description...


This is what I don't understand. How is the water supposed to be drawn through the hole for the sponges when there is also a hole directly in the pump chamber? Sure, some will but the main water course is going to go the way of least resistance. It just makes no sense to me but that could easily be that I just don't understand. Personally I think it may be just a bad design. Another thing is that the divider between the ceramic/carbon and pump sections is lower than the water level. Again, going with least resistance, the ceramic/carbon section would do nothing as the pump would just take the water from across the top of the divider and the hole in the pump section. Is it just the disturbance caused by the pump rather than actual water flow that causes the filtration or is this a bad design?


Like I've said I've never used this kind of filtration and do not understand how it can efficiently function.
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Old 05-16-2022, 02:56 AM   #8
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Maybe a diagram would help visualise your filtration if you could post something.

From what you have said i dont really understand what the inlet in the last section is for. Possibly its in case something clogs up in either of the other 2 sections and stops water flow and this inlet would then ensure your pump doesnt drain the last section, causing the pump to run dry and potentially overflow the tank. Like i said im running a new tank similar to yours and i have no input in my 3rd chamber.

Where is the input between your 1st and 2nd chamber? If its down at the bottom then water will flow through that 2nd chamber from the bottom, upwards, and then over the divide into the 3rd chamber.

This is the flow diagram from the manufacturer for my tanks filtration.



Perhaps you can find something similar for yours that would better explain how yours is intended to work. Maybe an email to the manufacturer.
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Old 05-16-2022, 04:14 AM   #9
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Your diagram shows a very different setup. I can't find a flow diagram for my specific tank but it is not like yours. The way mine is setup there is always a direct source of water for the pump that does not even involve the filtration. Of course the flow is going to go with the least resistance.


I would need to pretty much tear everything down to see where the first and second in/out happens to be... Hmmm, I suppose I could just pull the sponges and feel for the transfer point.


One thing I've noticed is that if I just use the air risers for the UG filtration I can see bubbles coming up through the back sponge filter. If I go through the built in only I see nothing in the sponge area. Even though under powered I think that my under gravel is doing the better job.


I am thinking about plugging the inlet that goes directly to the pump cavity and enlarging the inlet for the sponge intake. That MIGHT make the built in filtration system a little bit effective but there would still be the issue of the free overflow between the carbon/ceramic to pump sections. I think it is just a bad design.


Here is what I am thinking. I'm going to add another Whisper 40 air pump and run each full blown to each riser. Plug the water intake in the built in pump chamber and replace the current 264 GPH pump with a 100 GPH pump. This would give me a strong UG filter with also pulling enough water through the ceramics to mayhaps allow a secondary bacteria level.

I know that I MAY be put down for what I'm thinking but I know and understand UG filtration and the built in system makes zero sense to me. I want to maintain flow through the built in but just don't trust the setup.


Sigh, I would LOVE to cut out the plate between the main tank and filtration area and increase the usable tank size but am afraid that it may be a structural support panel. I'd hate to remove and have the tank blow out.


If you want I can use your above flow diagram and modify to show the difference but I think the filtration on my tank is just poorly designed. I mean how can you have filtration when there is always a direct connection from the input to the output pump?
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Old 05-17-2022, 12:27 AM   #10
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I got the second Whisper air pump today and finally have the kind of air flow I want. The following image shows the air flow I now have and I'm using two under filter filtration with each having it's own air riser and pump. If you understand anything about physics you will see that this kind of air flow will move a LOT of water through the gravel base. There will actually be more water going through the gravel than the 264 gallons per hour built in pump would put through the filtration media as the built in filtration setup seems like garbage to me. I mean probably 95% of the water flow does not even touch filtration media In this case I'll stay old school. I'm not putting down the concept of the built in filtration, I'm really not. I just think that the way it was done in my tank was a really poor design and I'm much better off using my under gravel system.I'm using fine air stones in the air risers as I just think they look better than the bubbles from a plastic grid stone. It there is ant difference between the air volume between the two it would be extremely trivial.


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