What makes a skimmer too small?

[WilRams]

I can how a skimmer can be oversized running a tank too clean but what makes one too small? Is it just skimmer cup filling too quick? Not enough contact time?

 

I ask because originally I wanted to run 2 separate systems. After much thought it will be much cheaper to tie both tanks into one sump. I don't have to buy double the equipment and gain the stability of a larger system. The skimmer (Nyos 160) I currently have is running on a 100g rated for 250g. It will eventually be tying into a 220. I figure I can get away with running it for some time until stocking levels force me to upgrade?

[treesprite]

Good question. I think choosing a skimmer involves so many factors that manufacturer ratings are only minimally helpful. The best way to figure out what to get is by consulting with at least 20 different skimmer-savy WAMAS members who have had experiences with a wide variety of products.

[epleeds]

If it's rated for 250, that's probably on a light bio load. I would guess 120 heavy stocked. You add 220 gallons more and you skimmer won't be able to keep up.

 

Time to upgrade to the NYOS 220. Rated to 500 gallons.

[madweazl]

I stopped looking at everything except for max air draw. I then look at the skimmers "rated" for my volume of water and look for an air draw rating that is highest. For comparison sake, my Bubble Magus Curve 5 has a max around 300lph where the Vertex 150 is around 900lph! Based on that, I figure anything 600+ should be a strong performer (this was for a 75g).

[Origami]

Justin from Avast (ctenophore here on WAMAS) said someing about this a few years ago. My recollection may be faulty, but I think that he said you should target the full volume of water going thru the skimmer body with a minimum contact time of 30 seconds. This would imply that the volume of the water in the body should be at least 1/120th the volume of the water in your tank. Again, this may be wrong, but the essence of his answer was one of turnover and contact time with the bubbles in the skimmer.

 

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[Origami]

Here it is (from Justin). My numbers were off but the idea was correct.

 

How does one size a skimmer based on total aquarium volume? I have a friend with a 300 gallon tank, no skimmer, and I want him to get one. How is this math calculated? Is it just gallons per hour thru the skimmer? What happens if the skimmer is smaller than would really be best? Is it just a function of dealing effectively with the skimmate?

 

The man is not going to buy one of these behemoth, very expensive. models but needs something. Please advise. Thx

 

I use Escobal's formula for skimmer contact time. The rule is roughly .75x/hr of water throughput, where x=total system volume. So our 200 gallon rating for the CS1 assumes about 150gph through the skimmer. Ideally you would have a 2 minute dwell time in the skimmer body for optimium contact of bubbles with organics-laden water. 150gph = 2.5gpm, or roughly a 5 gallon skimmer body volume. The CS1 isn't quite that big, as realistic space constraints do factor in. Also, more efficient pumps capable of producing more and finer bubbles help offset the chamber size. In short, adding even an "undersized" CS1 on a 300 gallon system will help a whole lot compared to no skimmer, since budget is a factor. You could increase throughput to 225gph on the CS1 without a problem.

 

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[WilRams]

Time to upgrade to the NYOS 220. Rated to 500 gallons.

That's the plan! I really like this 160 so I have my sights on the 220.

 

  

Here it is (from Justin). My numbers were off but the idea was correct. I use Escobal's formula for skimmer contact time. The rule is roughly .75x/hr of water throughput, where x=total system volume. So our 200 gallon rating for the CS1 assumes about 150gph through the skimmer. Ideally you would have a 2 minute dwell time in the skimmer body for optimium contact of bubbles with organics-laden water. 150gph = 2.5gpm, or roughly a 5 gallon skimmer body volume. The CS1 isn't quite that big, as realistic space constraints do factor in. Also, more efficient pumps capable of producing more and finer bubbles help offset the chamber size. In short, adding even an "undersized" CS1 on a 300 gallon system will help a whole lot compared to no skimmer, since budget is a factor. You could increase throughput to 225gph on the CS1 without a problem.

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Ok that makes sense comes down to contact time. Thanks for digging that up.

[madweazl]

I'm not quite understanding the math here. Is this suggesting you want roughly 75% of the volume running through the skimmer per hour?

[Origami]

Yes, but water that flows in also needs to be in the skimmer for 2 minutes before exiting. So it's mostly about achieving sufficient contact time with the air bubbles. See Justin's math. Once you have the flow rate in gallons per hour, convert to gallons per minute then double that number to get the skimmer body size. I assume that this assumes a lot of fine bubbles in the chamber but am not sure how that's accounted for here.

 

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[madweazl]

How the heck do you figure out the GPH (spec is hardly ever listed)? This isnt something you see very often on skimmers.

[Origami]

It's easier with a recirculating skimmer. In that case, it's the feed pump rate. For a non-recirculating type, it's probably tough because few people actually test or disclose those numbers. You used to be able to find threads where hobbyists tested air flow and water flow numbers for various pump/impeller combinations. That was a while back when it wasn't uncommon for people to build their own skimmer because good ones weren't easy to find.

 

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[paul b]

Is my skimmer to small?   I built it to go with my boiler temperature gauge on the wall   

 

[RJT]

Nice skimmer.  What pump do you have running it?

[paul b]

It runs on 2 pumps. This one ran for about 20 years to run the venture valve but I thought I needed a stronger one so I had a much stronger pump laying around and I use it now.

 

This pump is even older than that and pumps water from the tank into it.

[zygote2k]

Output of a typical cs1 recirc seems to be about a half gallon to a full gallon per minute using an mj600 feed pump.