Saltcorner: Review: C-Skim 1800

There's been much discussion as to the value of protein skimming over the past 10 - 15 years, all of which resulted in that the process is an extremely important component in what is universally considered the aquarist's most important goal, i.e., maintaining high quality seawater! I should also add that I've been a major player in those 'discussions' along with writing about the process itself and testing some of the skimmer models available in the marketplace. And when Red Sea asked if I would be interested in testing their new C-Skim 1800 model, I of course said yes, as I've seen it advertised and really wondered if it was all it was said to be. Keep in mind that over the past couple of decades I've seen skimmers of all sizes, various prices, and wonderful advertising claims, some that were not anywhere near being worth their price or claimed results. And since I didn't initiate this product test, made it clear if I found faults or inadequacies with the unit, no review would see daylight until they were corrected. With that very clear, Red Sea said, 'check it out and tell us exactly what you think,' as they wanted a review from a totally independent and well experienced source in the hobby, not a source tied to advertising or selling the product. With that resolved, decided to give the product a test that in my opinion would be more than just the standard 'hook it up to an aquarium and wait days for a result!' Before discussing the actual test, first a little background on the skimming process, then the unit itself.

Skimming Process

Mother Nature uses the skimming process to care for her oceans! The foam developed by waves crashing over reef crests or seen when waves roll onto beach sands and leave foam at their high point on the sand are the end result of the protein skimming process. It's that foaming process, i.e., a method that involves a special group of unwanted compounds called 'surface-active' compounds or 'surfactants' that tend to collect near or on the water surface because they are bipolar. Their hydrophilic or polar ends prefer to face water. Their hydrophobic or non-polar ends are attracted to air. Hence, accumulating Dissolved Organic Compounds including toxic organic substances such as terpenoids from soft corals and/or Caulerpicin from macroalgae are attracted to the water's surface or that of the air bubble, where it can be removed/exported from the aquarium's water via the 'foam' produced.

The result, especially in aquaria is much improved water quality! In fact, it's the reason why water used in the process should come from areas near the aquarium 'surface!' Other benefits are also received from the skimming process, e.g., it helps to maintain reasonable pH levels, reduces nitrate accumulations, oxygenates the water, reduces excessive carbon dioxide levels helping somewhat to minimize unwanted algae, and reduces the accumulation of un-needed heavy metals. A small deficiency, such as reducing levels of some valuable trace elements, can easily be overcome with the use of trace element additives. In short, it's the aquarist's most valuable tool in their quest for acquiring their most important goal - excellent water quality!

Before leaving this foam aspect, every quality skimmer has a pump size recommendation for optimum performance. But location of said pump is of all importance if the product is to deliver optimum performance! All to often the manufactures recommended size pump is mounted at a far distance from the skimmer input connection, possibly with some twists and turns in the delivery piping plumbing. Additionally, some pumps are mounted a distance below the protein skimmer, forcing the pump to work against gravity to raise its water output. Either way, less than the recommended amount of water output per its rating reaches the skimmer, negatively effecting skimmer performance. Not the fault of the skimmer, but that of the person who installed the product. Therefore, take into consideration the plumbing of the unit, and if need be purchase a larger pump as its always easy to throttle back the flow if excessive with a control valve, but impossible to increase it if too little!

C-Skim 1800 Features

Height 21.25 inches (54 cm); footprint (including installed aspiration pump) 13.4 x 10 inches (33.5 x 25 cm).

The unit can either be placed in a sump or as a standalone unit outside the system where convenient.

Additional Supplied Items

Mounting Base Pad

Clear hard plastic pipe for extending flow from outflow elbow - 6 inches (15 cm)

Outflow 90° Elbow - 1.5 inches (40 mm) w/air bleed-off nipple - (fits metric or imperial sized pipes because it has a stepped insert)

Flexible plastic hose - for connecting water pump to unit inflow connection - 5/8 inch (17 mm) x 24 inches (60 cm)

2 lengths of air hose - 24 and 6 inches (60 and 15 cm)

PSK Aspiration pump w/Aerostar pinwheel impeller for injecting 200 gallons of air (800 liters) and re-circulating interior water

Required - but not supplied

Contains a recessed viewing window (FoamView) providing a clear view of the foam rising in the neck of the skimmer. One could say the inset cuts down on the volume of liquid the cup could contain, however, would find that an inappropriate comment as aquarists realize that liquid needs to be monitored as needed per the environment of their aquarium. For those that tend to put off emptying the cup, there's a drain connection in the lower right front corner that can flow accumulating wastes to a separate collection container that can be sized as needed. Also, the cover of the collection cup is vented to allow air from within the skimmer body to escape, insuring there will be no backpressure from the injected air and that fresh air will always be circulating within the body of the skimmer. Collection cup can be removed without shutting down the unit! (See Neck Washing below)

One of the more interesting aspects of this unit is that its body/reaction chamber is canister filter-shaped with similar side latches and made entirely from an opaque plastic material. Gone is the viewing of the air and water mixing in the reaction chamber, which I had used on some other brand skimmers as a way to judge the quantity and quality of air bubbles being introduced into their reaction chambers. Actually, when this unit was up and running it became exceptionally apparent there was an enormous amount of correctly sized bubbles, about 1 mm, as its FoamView window quickly filled with bubbles! I can honestly say there will be less maintenance time keeping its body inside areas clean, as there will not be any algae growing on these surfaces as there are sometimes with clear body skimmers! As for its side canister filter-like latches, its quite simple to pop them open and remove the upper collection cup to gain access to its interior if need be, which might be once a year to do a thorough cleaning of its interior areas.

Peripheral Flow-Closed Loop Skimming

Nice sounding words, but had to see and understand just how the interior water flow was designed! With the Collection Cup removed, I found a conical shaped deflection baffle that encompassed most of the internal circumference of the top of the base unit. Its purpose appears to be two fold - to collect the building foam on its underside and guide it upwards through a central circular opening that aligns with the collection cup, and second, deflect the incoming water directed at its upper surface and force it downward around the small space between its edges and the interior walls of the unit. This downward water flow then passes over the air bubbles entering the skimmer body from the aspiration pump, increasing their dwell time. Keep in mind the aspiration pump is also withdrawing water from this chamber and mixing air into it, then injecting an air/water stream into this already circulating water flow! As for the water exiting the skimmer body, it's collected at its base where it is virtually bubble free and then flows through a vertical internal standpipe to the units outflow port. A very well thought-out process of air and water flow within the unit!

All levers/control handles and fittings are located on the front side of the skimmer, making it easier to control the items of your choice. The air control valve - controls the air flow to aspiration pump; water outlet control lever - controls the water level in skimmer collection neck; and, neck washing lever - described below. Very simple - only three controls!

Neck Washing System

Besides the innovative interior flow design, this item adds great value to the product! Along the entire top edge of the Collection Cup's central foam collection neck there's a snug fitting hollow plastic ring that is connected to interior pipework that allows incoming aquarium water to be diverted to it when this feature is to be used. When its control level, located on the outside of the upper left side of the unit's base is turned 90 degrees counterclockwise, incoming water to the unit is then diverted to angled holes in this so-called 'spray ring' that wash interior neck surfaces below clean of collecting sludge. It's recommended this aspect be used once daily to keep the neck interior clean. Sludge material washed away is simply deposited somewhat below in the foamy water and will be removed by collecting foam once the lever is returned to its off position. And that off point is locked in; as the level lip slips into a notched slot you can feel and hear when it's back to its normal/off position. Should you want to remove the Collection Cup for some reason and not shut down the skimmer, simply turn the level 90 degrees clockwise. I've tried it on the test unit and it works perfectly! An extremely nice feature, and something found only on some 'very' expensive protein skimmers!

Aspiration/Interior Water Circulation Pump

As mentioned above, the unit uses one of the best aspiration pumps available, however, unless one understands what distinguishes poorly produced foam from what is considered excellent foam, it's difficult to judge the results rendered. Bottom line, resulting foam 'must be' of the right constancy, i.e., remain stable (bubbles not quickly breaking) long enough for rising bubbles to push it to the point where it can slowly flow into the collection cup. Stable foam is referred to as 'dry' foam. Dry foam remains as bubbles for ten to twenty minutes at the upper edge of the reaction cylinder and in the collection cup. At a minimum, the foam's bubbles need to last long enough so their coating of surfactants can drain into the collection cup. If foam bubbles break within a few seconds of reaching the top of the reaction cylinder, it's referred to as 'watery' foam, which deposits most of its adsorbates back into the aquarium instead of the collection cup and also wastes a lot of water aquarium.

Supplied air tubing connects to an inlet port at the bottom of the pump and from there to an air chamber located on the right upper front of the skimmer body. At the top of this small air chamber there's a small fitting and control valve that can adjust the volume of air entering the aspiration pump. Without a doubt, the process within the body of this model skimmer has been perfected, as its foam production is perfect! And should the user want to drain the entire unit to move it elsewhere, its not necessary to pick up the full unit as there is a drain plug on the lower inlet to the pump, allowing for interior unit water to be drained to that level.

My first action was simply to remove the skimmer box from its shipping container, which had one of its corners completely bashed in and which was left on my back porch the night before. I immediately thought it might be damaged, but when opened the skimmer box within was in perfect shape. In fact, it was evident that it would take a gorilla to damage the skimmer itself, as the unit is totally surrounded by a few inches of Styrofoam! Except for installing its Aspiration pump, its outflow 90° elbow, and some airline tubing, which were securely tucked elsewhere in the box, the unit is basically ready to go. Reading the enclosed User Manual was next, which I found quite accurate and helpful. It suggests a 400 - 450 GPH pump be used to supply its water flow, which my test confirmed was the ideal size. But as mentioned above, if its water supply cannot flow from within a short distance it may be advisable to equip it with a larger pump.

The unit could have been attached to a 400 gallon reef tank that is constantly skimmed and has excellent water quality. However, that would have required a waiting period in my opinion of several days to make a complete assessment as to its overall operational capabilities. Instead, I call a local shop and asked its owner if I could set it up on his 600 gallon live rock system, as that would already contain a good measure of organics and hopefully produce a quick result that would help judge the units capability. Good idea was his answer along with that he would be interested in seeing this model skimmer working! I then attached the few loose parts and took it to his shop. Even though not overly pretty, the actual setup there took all of only a few minutes.

It just happened that the rock tank had a 450 gallon water pump circulating water within it. The skimmer was placed on a Styrofoam shipping box top that straddled two rock bins and its short 2 foot flex hose was attached to that water pump. The pump was turned back on and 'presto,' water began to overflow into the collection cup. Flow was throttled back somewhat and next the aspiration pump was turned on. Foam almost immediately began to show itself in the FoamView window. A slight adjustment to the outflow was made and the foam level stayed steady in the window. We were both impressed! About 5 - 10 minutes passed as the owner and I walked around his shop to discuss various other things in his many aquariums. When we came back, the skimmer was 'already' producing 'dry' foam as can be seen in the photos. In fact, both the shop owner and I said at exactly the same time - WOW, what perfect foam!

I then turned the Neck Washing lever to its 'wash' position to checkout that aspect and it worked flawlessly. Then turned it to the Cup Removal position and removed the Collection Cup without turning off the pump. We were both very pleased with its performance and over the next hour or two we compared it to other brands and came away saying the Red Sea C-Skim 1800 is not only excellent, but may be the best on the market for a unit of that size and price range.

There's also another factor I want to bring forward in this review, as I applied it to the unit being tested so as to make a judgment call as to its ability to skim various size systems of different complexity. Its noted on the product box/manual the unit can effectively skim fish-only tanks of 450 gallons, soft coral tanks of 300 gallons, and stony coral tanks of 150 gallons. To verify this, I used what is known as a Purity Coefficient, which must be applied to the actual outflow from a correctly operating (foam producing) unit. That's easily accomplished by judging the amount of time it takes to fill a container of given size and deduce how much flows out of the product in 60 minutes. In this case, using a 2 gallon pail, it was quite messy and a good thing the shop floors were bare concrete! Once outflow is determined, it can be judged how often the unit will filter 99.99% of the water in the system by applying the correct purity coefficient. Where the test unit was concerned, a 450 GPH pump was utilized inline and only 2 feet from the units input connection. Outflow was at least 400 GPH. If I were to apply this similar hookup to a 150 gallon tank, it would filter 99.99% of its water about every 3 hours and 45 minutes. If the tank were 450 gallons, it would filter the entire tank's water about once every 10 hours. If the tank were 300 gallons, it would filter the tank's water approximately every 7 hours. All are reasonable turnover rates for said size tanks, even if highly loaded. If concerned about over-skimming, the operation time of the skimmer can be cut back, however, nighttime operation is always the best time to run a skimmer because of its oxygenating capability! I came away highly impressed, but slightly damp!

There is not one item that cannot be easily disassembled or replace if need be, even replacement o-rings are available. Probably only the interior of the reaction base unit is somewhat difficult to clean, as its baffle plate will have to removed completely for full access and that would require the Neck Washer valve to be removed, which would take a few minutes to accomplish. Nevertheless, it's possible for a long handled foxtail brush to be inserted through the baffles central opening and also around the space between the plate edges and wall of the skimmer body. Therefore, interior reaction chamber cleaning could mostly be accomplished quite quickly if need be. As for completely dissembling the product for cleanliness purposes, I see that rarely being needed. As to daily needs, connecting a drain line to the Collection Cup will far reduce the time needed to monitor cup liquid level, and the Neck Washer system if used regularly as noted in the User Manual will far reduce the need to hand wipe the foam collection neck area!

In closing, I've not seen better foam production! You definitely get your monies worth with this product!

(The C-Skim 1800 became available in 2011 and was discontinued in 2019, and during that timeframe, considered it to be one of the best skimmers, if not the best I ever had during my past thirty-five years of marine aquarium keeping!)

C-Skim 1800 - Product Review

Manufactured by: Red Sea