UV Sterilizer set-up: flow rate query

[islandguy11]

Hi I'm going to install a new Eheim Reeflex UV500 sterilizer on my 80 gallon freshwater tank with showpiece Kamfa. I don't really need it all for algae or water clarity, main function will be bacterial/parasite control. Overkill perhaps, but he's cool enough to deserve the extra protection.

I plan to use a powerhead filter to pump tank water down to the sterilizer, which will be attached to a thick wooden board below my tank. A 3-4 foot return line will take the water up and back into the tank.

I understand that if the pump/powerhead were below the tank, one could lose anywhere from 50-70% of the unit's GPH rating. So if my sterilizer needed only 105 GPH to achieve true Level 1 sterilization, I would need a pump that was about 200-250 GPH depending on a few other factors.

So my main question for those of you who are better at engineering/physics: what if the pump/powerhead filter were in the tank and pumping down to the sterilizer? Given that it still has to pump the water back up on the return side would I still lose 50-70% of a pump's rated GPH (as it entered and went through the sterilizer), or would it be less GPH loss given the initial help of gravity?

Also, once established, would such a loop main a relatively consistent water flow throughout the system, or would it go faster on the down side/going through the sterilizer, then slow down after exiting and on the way up?

Thx in advance for any input.

 

[squint]

Is the water going to be filtered before it enters the UV? I would just put it behind whatever filter you have and not worry about the flowrate.

 

[islandguy11]

Is the water going to be filtered before it enters the UV? I would just put it behind whatever filter you have and not worry about the flowrate.

Relevant question Squint and I should have clarified: actually my main filter is an internal, overflow corner filter (like those very popular in Thailand/SEA). They're quite effective but not easily adaptable so I can't easily pre-filter via that like one could from a canister filter.

Instead I'm just going to use a power head with attachment containing coarse foam and poly-fil -- not super ideal I know but my tank is bare bottom and water kept quite clean and clear, so I'm thinking/hoping it should be sufficient. Also forgot to mention as per Eheim recommendations I'm aiming for 400 L/H to target microbes.



Which I plan to put about where my fish is in this pic, as this is directly downstream from where that corner filter pumps on nice clean water.

 

[Drstrangelove]

I understand that if the pump/powerhead were below the tank, one could lose anywhere from 50-70% of the unit's GPH rating.

I've never heard this. Sounds like someone is guesstimating or SWAG-ing. Loss of the "base" GPH rating might be 100% or closer to zero depending on the pump. The height is a factor, as bends in the line, the type of line (materials have different amounts of resistance to fluid movement), the smallest diameter of the line, etc. But different pumps have different GPH curves. They don't follow a general rule of loss.

Pumps with identical "GPH ratings" might produce grossly different outputs at various heads even if everything else is exactly the same. If you want 105 GPH at 4 foot of head, you want a pump that is rated for 105 GPH at 4 foot of head.

So if my sterilizer needed only 105 GPH to achieve true Level 1 sterilization, I would need a pump that was about 200-250 GPH depending on a few other factors.

Besides looking for the appropriate rating for the head you are expecting, you might want to revisit the decision to place the UV under the tank, since I assume you don't have a sump. If water is flowing out of the tank from a gravity overflow to a sump, it can't drain the tank even if the pipes from the overflow come loose, since the water will stop flowing out once the level in the tank drops below the overflow. And if the sump is properly set up, the water will fill the sump or overflow into a drain.

If you place the power head where the fish is and have it pump out of the tank, the tank can drain to that point from the power head if you have a leak or might simply siphon if the pump stops working.

 

[TwoHedWlf]

I understand that if the pump/powerhead were below the tank, one could lose anywhere from 50-70% of the unit's GPH rating.

Except it doesn't work anything like that.

You have a closed loop, based on your description. The only height that matters is how far the outlet is above the surface of the tank's water. So the only flow you'll lose is due to friction in the pipe. You have 0 static head.

Unless your intention is to raise the outlet 3-4 feet above the tank and let it spill from there.

 

[islandguy11]

Great info Drstrangelove, much appreciated! I mostly got that from an American Aquarium youtube video on the subject, but now I realize that the 50-70% guesstimate is simplistic in light of your info and really I'm just going to have to carry out a few tests with different power heads to obtain desired flow rate.

Thx too for highlighting the safety factor with my current approach, which I wasn't fully considering... In fact I've been playing with the idea to add a sump (for mechanical filtration; I stupidly wasn't thinking about overflow), but have never used one before and they're not easily available here so it would have to be a DIY project gleaned from youtube, which I'm ok at but not great.

If I did make a sump (and with no drain around), approx. how many liter capacity sump do you think I would need to prevent overflow if tank is 80 gallon (L48" X W22" X H21" with little decor)?

Because there's also the issue of this tank is on the second floor (of a long-term rented house) and on nice hardwood flooring (which is covered by some vinyl mats around the tank area). While the house isn't that old and pretty well-made by Thai standards, I'm not sure I'd want to add the extra weight of a sump under my tank. (in which case I guess I'd have to lay that power head horizontally and closer to top of the tank).

Would it be any safer if instead of using power head in tank I used a (low flow rate) canister filter below the tank and before the UV sterilizer?

Thx also TwoHedWolf for your contribution, which further clarifies the issue, I wish I were smarter about such things but at least have a great source of help in MFK members.