Skimming conversation

[Scooterman]

Nikki, I have mine at the last stage before going back up, but the outlets are dumping back to the first stage of my sump, only because a lack of space. I think it was mentioned that reskimming was a good thing because the finer particles would get another chance to skim up!

 

[ldrhawke]

I have the skimmer set up in the first compartment on a little acrylic stand (to the recommended water height for the skimmer), right where the water comes into the sump. The water comes out of the skimmer in the same compartment, so that is where my question lies. I get a ton of nasty skimmate, so recirculating some water must not be that bad. Does anyone set up their systems to "double skim"?

Here is an image of my skimmer set-up....maybe a visual will help. I wouldn't want to change the outflow, as I figure ER designed the skimmer this way for a reason. But I'm curious as to whether or not any of this makes a difference?

Nice installation...how do you keep it so clean

The answer on your set up is dependent on the rate of overflow water from the tank. I would imagine you are putting two or three times the amount of fresh overflow from your tank compared to the flow out of the skimmer into a common sump. So, most of what the skimmer sees is mostly fresh material to skim and 25% to 35% at most is being recycled. It would probably improve your skimmer efficiency a little if it only saw overflow, but it would probably complicate the skimmer discharge piping more than it is worth.

 

[ldrhawke]

Added comment.....it would be an interesting test to add another T and valve up stream in the overflow line so you could divert part of the overflow into the compartment on the left side of the skimmer.

If you diverted 1/2 the overflow you would be recycling twice as much out of the skimmer compartment in the skimmer. If you stopped the flow into the skimmer compartment you would be recycling 100%. This would make it more like the new recycling skimmer that ER states is more efficient. It would be interesting to see the effect recycling has on the quality and amount of skimmate and the tank water quality over a few months. :?:

 

[DonW]

Nikki,
I think as long as your skimmer pump and return pump are sized in proportion to each other your fine. Your skimmer looks to fit real nice in the sump and takes up most of the chamber. There should'nt be much getting past it.

Don

 

[Zephrant]

Good pints Colin- I agree that a balance between contact time and water flow is important.

Quick note- if the Beckett skimmers available in your area are "very noisy" then they are not well made. A well designed Beckett is not silent, but is certainly no louder than the pump that runs it. I ran one for a while on a Sequence 3600, which is a very quite pump, and I could not hear the Beckett injector unless I put my ear right next to it.

As for "very expensive and powerful" pumps, I don't feel they are much worse- The Sequence 3600 is 160 watts. Not bad for a pump that runs 600+ GPH though a Beckett. Granted it is more than a single Eheim, but perhaps not more than a four pump Needle wheel, which is about the area it could be considered equivalent.

The air-stone idea is neat- I'd like to see what kind of air flow rates you can get. Hook it up to the 5hp compressor, and see what it takes to blow the top off of the skimmer.

I still believe that the "whirling" idea is a bunch of bunk. There is a fixed amount of water going in and out of the skimmer. If it is whirling, it is merely moving faster, it is not taking "longer" to exit the skimmer. If any portion of the water took "longer" then an equal portion must exit the skimmer faster, or it would overflow the neck.

Swirling is not at all the same as adding a taller or wider tube.

Some manufacturers just don't do physics well.

As you mention, spinning the water fast causes the bubbles to congregate on the inside of the vortex- Simple centrifugal force forces the heavy water to the outside, which collects the bubbles on the inside. You can see the effect in some of the cheap vortex skimmers available. I've often considered using that effect to make a bubble extractor for overflow returns, but have not come up with a workable plan yet.


Nikki- I would not worry about it too much. In reality you are only getting a few percent of water that recirculates though the skimmer more than once. And hey, aren't we all talking about skimmer designs that recirculates being cool?

Zeph

 

[ldrhawke]

Added comment.....it would be an interesting test to add another T and valve up stream in the overflow line so you could divert part of the overflow into the compartment on the left side of the skimmer.

If you diverted 1/2 the overflow you would be recycling twice as much out of the skimmer compartment in the skimmer. If you stopped the flow into the skimmer compartment you would be recycling 100%. This would make it more like the new recycling skimmer that ER states is more efficient. It would be interesting to see the effect recycling has on the quality and amount of skimmate and the tank water quality over a few months. :?:

The more I think about the difference between a recirculation skimmer and one sitting in a sump, I'm not sure if there is any signifcant difference. Both are recirculating the whole system in either case.

 

[NaH2O]

Thanks for all the insight - I knew Euro-Reef had a new design coming out, but didn't pay attention to see what it was all about. I wonder what kind of improved performance they were seeing with the recirc. design, and what the cost difference will be. Your point on recirculating the whole system does make sense to me. It all goes through eventually. For what its worth, according to ER's website, my skimmer (CS8-3) is rated for ideal aquarium 175 gallons (I have a 120 gallon + sump + fuge). How do the skimmers get rated anyway? - What types of things do the manufacturers look for when determining "ideal tank size" for a given skimmer (apologies if this was answered already - just point me to the post)?

LDRHawke - Love your tank! How do you like the CPW?

 

[ldrhawke]

LDRHawke - Love your tank! How do you like the CPW?

Thanks... When I came up with the CPW idea I hoped it would solve the export and phosphate over load potential issue with a DSB. CPW works and pulls a lot of waste through a DSB, but with my fish load, I still had phosphate issues that retarded SPS growth. RowaPhos solves the problem but I am always looking for a better way. I still use the CPW system but only for water changes.

I've become a believer in skimmers, like many others. I am in the process of building a new skimmer, that I hope will be more effective. In addition, I'm testing a modified version of the Zeo concept that I hope will increase the efficiency of removing phosphates and be simplier to apply. The idea will be to improve upon phosphate exporting even further so that heavy feeding doesn't start to store phosphate that will later come back to bite you. I am very pleased with results after 60 days. I purposely left two small clumps of Bryopsis as a 'canary in the mine". It is slowly turning white like cotton candy and the Tangs are starting to feast on it. I'm going to take it slow and will use it for at least 6 months to a year before I get into any details or recommend it......as reefers say, "only bad things happen fast in a reef tank" :badgrin: I want to make sure it does give me any surprises.

Bomber on RC was right....the key to successful reef keeping is getting as much waste out of the tank as possible to start with and not trying to biologically treat it in the tank. The more bacteria you grow in the tank, the more phosphate is stored somewhere in a pile of dead bacteria bones.:badgrin: This is why skimming is so much more successful and widely used. It is the best exporting system out there. Especially, as I believe, if it is run on the wet side.

 

[dnjan]

Additional thought on wet vs. dry skimmate

On skimmers in which the air intake is driven by water flow (for example, venturi skimmers), wetter skimmate is produced by increasing the air flow. But air flow is accomplished by increasing the water flow. More water flow means less bubble-water contact time in the skimmer. Less bubble-water contact time means reduced organic removal. So skimmate that is too wet can be an indicator of less-than-ideal adjustment of the skimmer, and therefore less efficient performance.

Fine-tuning a skimmer is not generally an easy task, and often takes experience with the specific skimmer. I wonder if the amount of time that these skimmers are being run is sufficient for them to be fine-tuned for optimal performance.

 

[gobie]

Actually This Not Always True. I Had A 4 Foot Skimmer With A Masi Injector
Supplying The Air Intake It Produced A Ton Of Dry Foam When The Water Level In The Body Was 12" Or Less Above The In Take. I Would Have Kept The Skimmer But It Was Too Hard To Clean.

 

[ldrhawke]

On skimmers in which the air intake is driven by water flow (for example, venturi skimmers), wetter skimmate is produced by increasing the air flow. But air flow is accomplished by increasing the water flow. More water flow means less bubble-water contact time in the skimmer. Less bubble-water contact time means reduced organic removal. So skimmate that is too wet can be an indicator of less-than-ideal adjustment of the skimmer, and therefore less efficient performance.

I'm not sure if your assumption is correct. If I reduce the flow rate through my skimmer to increase contact time and to get a drier skimmate, compared to higher flow rates and less contact time, I don't believe I get better organic removal....overall.

The increased contact time may improve effiency of single pass but does not neccessarily improve total organics removal. Or to put it another way, removing less from more may be better using higher flow rates.

When I run my skimmer at higher air and water flow rates I get a wetter skimmate. I understand it may be removing less per pass, but I believe higher flows in my case maybe removing more total organics. Part of the basis of this opinion is that my ORP readings are higher with wetter skimmate, indicating more total organics removal. The problem is there can be so many variables that change performance;ie, the skimmer sizing, turn over rates, and organics loading. With undersized skimmers, you may be better off removing 50% per pass with high flow rates, than 100% per pass with low flow rates, if you can do it with more than twice the flow rate and remove 50% per pass.

I am modifying my Euro Reef skimmer to increase the volumetric size 3 times and have twice the flow rate, which will hopefully remove more organics per pass and have still have higher tank turn over...at least that is the idea. The modified skimmer will combine a pinwheel SEDRA 900 pump for recirculation and a downdraft using a Mazzei venturi and another SEDRA 900 for the feed on the same skimmer to hopefully improve performance. Just finishing up construction and I am anxious to see what and how much skimmate it can produce after I tune it in.

With a skimmer I don't believe you can put too large a one on a reef tank, where you are looking to remove as much of the residual waste as possible to have nuitrient poor water, only too small a unit. If you over skim, if that is really possible, it easier to add new nutrients than deal with the old ones that are starting to decay. At least that is my present opinion.

 

[dnjan]

Good points. But in my experience, the increase in flow rate between fairly dry and quite wet skimmate is not that much. So I don't think you really could use your "half the efficiency but twice the passes equals same removal" approach.

By far, the best improvement that you could make (and are making, if I read your post correctly) is to increase your air injection for a given flow rate. The Mazzei venturi is hitting that right on the head! It might be interesting, after your modifications, for you to throttle the pump feeding the Mazzei down, and see what that does to skimmer performance.

Also, I'm not sure I agree with your reasoning in "my ORP readings are higher with wetter skimmate, indicating more total organics removal". ORP readings don't directly indicate the level of organic removal. They indicate the oxidation potential of the water, which is influenced by dissolved oxygen (possibly from the increased bubble production in the skimmer) as well as the oxidation (or reduction) potential of dissolved organics in the water. Too complicated, IMO, to attribute higher ORP to greater organics removal.

 

[ldrhawke]

ORP and wet skimmate

Also, I'm not sure I agree with your reasoning in "my ORP readings are higher with wetter skimmate, indicating more total organics removal". ORP readings don't directly indicate the level of organic removal. They indicate the oxidation potential of the water, which is influenced by dissolved oxygen (possibly from the increased bubble production in the skimmer) as well as the oxidation (or reduction) potential of dissolved organics in the water. Too complicated, IMO, to attribute higher ORP to greater organics removal.

I agree using an ORP reading as a method to analysis anything is iffy at best. Even increase your S.G. and your ORP is affected and climbs. But, the ORP should increase with reduced organic material in the water which consumes oxygen. Just feed your tank or stir up the bed and the ORP will drop like a rock. The basis for my comment, is that I have noticed in my tank the ORP runs consistantly higher over days as I remove more wet skimmate and drops if I run it dryer. My air flow to the skimmer remains constant under both wet and dry conditions, the only change is the level in skimmer; so I don't believe it is caused by increased bubble production.

 

[ldrhawke]

Good points. But in my experience, the increase in flow rate between fairly dry and quite wet skimmate is not that much. So I don't think you really could use your "half the efficiency but twice the passes equals same removal" approach.

I should have qualify what I meant by flowrate. I am talking about the total amount of skimmate removed from the tank, not the flow though the skimmer. More tea colored skimmate may be better than less concentrated dark brown skimmate when removing organics, if the total solids and volatile solids remove are measured.

 

[dnjan]

I agree using an ORP reading as a method to analysis anything is iffy at best. Even increase your S.G. and your ORP is affected and climbs. But, the ORP should increase with reduced organic material in the water which consumes oxygen. Just feed your tank or stir up the bed and the ORP will drop like a rock. The basis for my comment, is that I have noticed in my tank the ORP runs consistantly higher over days as I remove more wet skimmate and drops if I run it dryer. My air flow to the skimmer remains constant under both wet and dry conditions, the only change is the level in skimmer; so I don't believe it is caused by increased bubble production.

Good information! Thanks. I've never watched the ORP display after messing with the sand. I did make some water-flow changes recently, however, and this moved some sand around a bit. ORP was a bit low for a couple of days.

 

[dnjan]

My air flow to the skimmer remains constant under both wet and dry conditions, the only change is the level in skimmer; so I don't believe it is caused by increased bubble production.

As a side note, changing the water level in the skimmer is indeed changing the flow rate, because you are changing the backpressure on the pump. As a rough approximation, a 6" water level change would be about a 5-10% change in water flow rate.

 

[ldrhawke]

The water level change in my skimmer to go from wet to dry is less than a 1/2" and it has little to no effect on flow rate.

 

[dnjan]

Wow! Talk about sensitive! I thought the change was more like a half foot than a half inch! Is it difficult to keep the level dialed in that precicely?

 

[Scooterman]

Yes, auto top off with a good float switch.

 

[ldrhawke]

Wow! Talk about sensitive! I thought the change was more like a half foot than a half inch! Is it difficult to keep the level dialed in that precicely?

It is PM Bullet skimmer outside the tank, which has been modified and made into a recirculation skimmer using a ER pinwheel pump. It is fed with a separate pump and an air ejector to increase air flow. The water level in the sump has no effect. The liquid height in the skimmer is controlled by the discharge pipe height setting, which is adjusted by rotating the unglued elbow slightly to vary the dischrge head. The water level in the skimmer fluxuates very little once set.

It has worked well, but I'm hoping with the even larger skimmer I'm making, with more bubble contact time, I can improve the organic's removal even more. Isn't bigger always better

I'm modifying a new Euro reef 5-2, that I bought on Ebay for $100, so that it will be similar to an EuroReef model 6-4, but will be 6" taller, 42" overall height, and it will use Sedra 9000 intead of the Sedra 5000 they use. It will be an outside the sump mount and also use a continuous recirculation system. So it will also have a feed pump, which I will have an air ejector on. After purchasing all these stupid parts, i'm not sure if I save any money over buying a new ER 6-4, but it's been fun.:lol: I just hope it foams...