the fine line with going 'plus 1' on skimmers

[igot2gats]

Let's just assume that the situation is creating a full blown SPS dominated reef.

Where do you draw the line as far as getting a skimmer rated for bigger than your tank? How high of a rating for the skimmer, compared to your tank is good/bad?

Even though SPS love clean water, too clean can lead to problems as well.

Thoughts?

 

[acabgd]

Would love to hear opinions as well. Although, isn't like 2 times the rated volume for skimmers widely accepted as being optimal? (as in 100g tank = 200g rated skimmer)

 

[igot2gats]

Would love to hear opinions as well. Although, isn't like 2 times the rated volume for skimmers widely accepted as being optimal? (as in 100g tank = 200g rated skimmer)

Right.

But what about a skimmer that's rated for 125 gallons for the 100g tank? Can the skimmer that's rated for 125 gallons still get the job done? This is where my confusion comes into play.

I understand that part of it is that you need to make sure you have enough head height (from top of the skimmer to underneath tank), so that you can take the collection cup off, etc.

But, assuming you have plenty of room under your tank, & the skimmer fits in your sump, can a skimmer that's rated slightly bigger than your tank still get the job done? What are the drawbacks?

 

[reefgeezer]

Ratings are so sketchy that using them to determine your skimmer selection is tough. Generally, IMO, high end skimmers are rated more accurately than lower end models. That said, it's the bioload not the water volume that matters. A 125 with no fish that's loaded with SPS might run well with even an under rated skimmer. Add a bunch of heavily fed fish to that same tank and even a high end skimmer rated at twice the tank's volume might not be big enough.

FWIW, I use a 2X rated skimmer and just feed more if the nutrient levels seem too low. It a mid-level brand so I'd guess it is over rated but I still have to up the food input every once in a while.

 

[Timber77]

You can't over skim your tank. I run a 6 foot aqua medic t5000 dual on a 165 gallon well stocked tank. Its rated around 1200 gallons. Only issue I have is not having any issues, it just works, the top of the skimmer always has a baseball sized ball of foam and as soon as i start feeding it starts skimming immediately. Short cheap skimmers might suffer if you get one with too wide of a neck from your bio load, but a good skimmer won't have this problem.

 

[wolfblue]

You can't over skim your tank.

I'm with you.

--John

 

[mc-cro]

I dont think you can overskim either. The skimmer just wont produce much skimmate if the waters too clean.

Its not like GFO or Carbon where you can actually strip the water column of all nutrients. A huge skimmer on a small tank just wont run very well and wont be efficient.

 

[slief]

You can't over skim your tank. I run a 6 foot aqua medic t5000 dual on a 165 gallon well stocked tank. Its rated around 1200 gallons. Only issue I have is not having any issues, it just works, the top of the skimmer always has a baseball sized ball of foam and as soon as i start feeding it starts skimming immediately. Short cheap skimmers might suffer if you get one with too wide of a neck from your bio load, but a good skimmer won't have this problem.

While it is true that you cant over skim your tank, the issue with an oversized skimmer is that in many cases, it won't skim consistently. Skimmers such as the Bubble Kings have very large diameter necks on their larger skimmers. If you choose too large of a skimmer for your bio load, you have to adjust them to skim very wet to get decent output.

Once they exhaust the nutrient level which will happen very quickly as they are very efficient, their ability to skim (even wet) will be compromised forcing you to adjust them further. Then the issue is that the skimmer will overflow from time to time as a result of being right on the ragged edge of wet adjustment. The end result is that in many cases, you will end up finding yourself adjusting an oversized skimmer more frequently and be prone to overflows.

As was noted earlier in this thread, many skimmers are over rated which is where the 2X theory comes into play. On the other hand, high end skimmers like the BK's are rated very conservatively and as such will not perform very consistently in low bio load (relative to the skimmers rated output) systems.

This isn't as much of an issue with less expensive skimmers that utilize a narrow neck design however with the high end skimmers with larger diameter necks, this become more of an issue.

That said, if you are going with a high end skimmer such as a BK or Deltec, it is wise to follow the manufacturers suggest tank size rating and don't over size your skimmer if you want it to skim like it is designed. I have an Alpha 300 on my tank and it skims like a well tuned machine but it is also properly sized for my bio load. I know of other that have used the same skimmer on much smaller systems/loads and not have as consistent of results. This was no fault of the skimmer, but rather the fact that there was not enough bio load to get a proper foam head going without having to adjust it too wet.

 

[reefgeezer]

Since we're in the Advanced Forum, I'd like to challenge the "can't over skim" theory... a little. I've argued the other side many times before, so it's a little strange but... IMO, the level of organics in the water column may be driven too low to support colorful, fast growing SPS corals before the skimmer actually shuts down. I think a well performing skimmer that is over-sized for bioload has the capability to take too much from the water column. Add carbon dosing used in many SPS systems and, IME, a tank can be over skimmed with even a less than optimal skimmer like my old Reef Octo. I can't imagine what a Deltec or BK would do.

That said, IMHO, it is still better to have a skimmer capable of over skimming and feeding heavily or otherwise increasing the bioload to ensure it doesn't.

 

[mc-cro]

Add carbon dosing used in many SPS systems and, IME, a tank can be over skimmed with even a less than optimal skimmer like my old Reef Octo. I can't imagine what a Deltec or BK would do.

I agree that scenario can cause a nutrient starved tank, but is that because of the skimmer or due to carbon dosing when its not needed or understood?

If your skimmer is really that oversized then you shouldnt need to carbon dose too??

 

[reefgeezer]

If your skimmer is really that oversized then you shouldnt need to carbon dose too??

Interesting thought and I don't have a definitive answer. Skimmers remove organics that would eventually contribute to nitrate and phosphate levels but don't directly remove them. Carbon dosing doesn't make the skimmer more efficient, it just creates organics that the skimmer can capture that also have bound nitrate and phosphate. Even if extremely efficient and over sized, a skimmer can't remove free nitrate or phosphate. It can however strip too many organics in an effort to keep nitrate and phosphates low.

 

[Timber77]

Ya, i can't dose carbon or I will get cyano, I guess thats a downside. However I don't need to carbon dose. Have not had measurable phosphates or nitrates in years. I quit testing for those about 8 or 9 years ago. I only really test for MG, CA, alkalinity and salinity. I have good circulation in the tank. I do run ozone on the skimmer (aqua medic 50 MG/hr) and think that helps with skim mate production and keeps ORP up a bit, I don't measure ORP either, just low dose of ozone so not too concerned with a mythical number. I think you need to start using centrifuge's in order to strip organics on a level that would be called "over skimming"

 

[Timber77]

Slief, are you saying my skimmer is not high end? It eats the atb i have on my predator tank for lunch . I never wet skim always dry skim, it only gets wet when I throw in a bunch of food, but that dies down in 10-15 minutes. The cup is about a foot tall but the neck size at the top drops down to maybe 1 1/2 or 2 inches wide. Thats the advantage of tall counter current venturi over needle wheel. Ive ran it on a bigger reef in the past, and it still skims the same on the smaller reef. I haven't really bought a newer skimmer in years except acquired an ATB in a tank setup purchase. Its a good skimmer for an in sump model, but not compared to a taller skimmer. The ATB has a wide neck and it doesn't always have a foam head up top like the T5000 dual does. It also can't dry skim. That tank gets fed 1/4 lb of raw shrimp every other day, and daily rods food. Its a predator tank with a couple larger zebra morays. I see what your saying, the ATB needs to be on a bigger heavily fed tank in order to keep a foam head, while the taller aqua medic always has a head , even on a tank thats officially way too small. After reading this thread I put the atb up for sale in the used section.

 

[SGT_York]

No his comment was on neck size, how you made that leap in your conclusion is a bit baffeling. The good thing about an oversized skimmer is it's much easier to add more food and livestock than to get a new skimmer or reduce the bioload.

 

[jerpa]

Once they exhaust the nutrient level which will happen very quickly as they are very efficient, their ability to skim (even wet) will be compromised forcing you to adjust them further. Then the issue is that the skimmer will overflowfrom time to time as a result of being right on the ragged edge of wet adjustment. The end result is that in many cases, you will end up finding yourself adjusting an oversized skimmer more frequentlyand be prone to overflows.

Isn't this a bit of user error though? Once the skimmer has been adjusted and begins to idle should it not be left alone? When the organic load in the water rises again the skimmer begins to produce, and because it wasn't adjusted it will not overflow. Do we have any evidence that consistent production through a smaller neck is better than the on/off production from a larger neck on a smaller system?

I have an SRO XP2000 EXT on the system below. It has an 8" cone body with a 4" neck. I currently have 5 fish, all under 4", and a very light coral load. My skimmer idles probably 75% of the time. It generally produces most of its skimmate in a few hours after feeding and in response to snail spawnings and such. If I were to adjust it to produce during the idle periods I'm sure I would run into issues with overflowing. Running the way it does now reduces nutrients enough that chaeto will slowly wither and die with no GFO use and 10% water changes every month.

 

[reefgeezer]

I think you need to start using centrifuge's in order to strip organics on a level that would be called "over skimming"

Over stripping doesn't have to be to zero in order to negatively affect corals. Remember, it's dissolved organics we are discussing. I read something a long time ago that suggested that much or the organic food that SPS corals receive is absorbed. The article suggested the level of organics in the water as compared to level in the coral determines how well the coral can do this. I think we can certainly drive organics too low with skimming, carbon dosing, ozone, & etc. in an effort to rid our systems of nitrate and phosphate.

Again, don't misread my argument, I do believe in aggressive skimming. I just think you have to recognize when you're removing too many organics and do something about it.

 

[igot2gats]

I see this in the description of skimmers. What does 'filtration demand' mean?

Filtration Handling
•100 Gallon - Light Filtration Demand
•80 Gallon – Medium Filtration Demand
•60 Gallon – Heavy Filtration Demand

 

[reefgeezer]

I see this in the description of skimmers. What does 'filtration demand' mean?

Filtration Handling
"¢100 Gallon - Light Filtration Demand
"¢80 Gallon "“ Medium Filtration Demand
"¢60 Gallon "“ Heavy Filtration Demand

IMO... It doesn't mean much. More of a tip of the cap to reality and maybe just a little better than a single rating. Unless it's a high end skimmer... 2X the "heavy filtration demand" rating.

 

[igot2gats]

Does it mean that you can stock heavy in a 60 gallon, and can only stock lightly in a 100g?

 

[reefgeezer]

Does it mean that you can stock heavy in a 60 gallon, and can only stock lightly in a 100g?

That's what the manufacturer in implying. However, the numbers provided usually aren't anywhere close to accurate. Think about it... who decides what is heavy or light? Your definition of light could easily be what the manufacturer considered heavy. The numbers might provide some reference but otherwise they are useless.