We have two skimmers to play with: the Fluval SK400 and the Oase CrystalSkim 350, to cater to 400-litre (380-litre in the EU) and 350-litre tanks (maximum) respectively. Here's what we found...
It would be unfair to call it a like-for-like comparison. The Oase model sells for around £45, with the Fluval available for closer to £20-25. And out of the box, you do get a sense for which is the nicer model. vlog kit
At first glance, the Oase is an attractive piece of kit, right down to the tasteful grey colour. Aesthetics appear key, with the CrystalSkim (I’m assuming) vying for the aquascaping market, where cool contours and minimalism are king. Even the bracket attaching it to the glass is beautifully machined clear plastic, easily removed for cleaning purposes.
At half the price, the Fluval SK400 does lack the elegance of the Oase model—more Carslberg than Château d'Yquem. Stark black and with a couple of red flourishes, this is a workhorse rather than objet d’art.
Using the CrystalSkim is intuitive enough. You position it so that the crown (the uppermost part of the float body, which is buoyant and bobs up and down over the skimmer proper) sits just clear of the intake protector. The intake needs to be submerged if you don’t want it sucking in air. You don’t want that, that’s when these things can get noisy.
There’s a flow control, but it’s pretty inconspicuous. The shaft on which the intake protector sits rotates around 45°, allowing you to fine tune how much water it’s pulling—you can reduce it from an out-of-the-box 300lph down to around 200lph. Pull off the protector and you can access the small sponge filter inside. An extra treat from Oase here; you’re provided with a pair of tweezers to help you extract the sponge from the housing. Keep it safe.
Water is released through a concealed, circular ring outlet at the bottom of the unit and, by gently pulling the cover of this from the main body, you have access to a small impeller. Again, keep those tweezers safe, for they are superb at fishing the little fellow out.
And that’s it. It’s smart, it’s sleek, it’s quiet enough when running, and it does the job. A stern critic might argue that the float body is quite short, only giving you about 4-5cm of ‘tidal action’ before you either need to move it down a bit or top the tank back up, but who’s letting their tank evaporate that much between water changes and top-ups? No wonder you’ve got issues with surface scum…
Setting up the SK400 is no trickier than the Oase model, and for those that do leave their tanks to drop right down in water level, there’s a lot more play in the floating intake.
As opposed to a concentric outflow, Fluval has opted for a traditional front-facing nozzle, making the output more noticeable, though that’s no bad thing. The vigour of the inflow at the top can be adjusted by twisting the red intake regulator dial on the top of the device, while outflow can be tweaked with the red flow control slider in the front of it. Don’t expect too drastic a reduction in flow.
Cleaning is where the SK400 becomes a little trickier. For one, tweezers aren’t supplied, so accessing the impeller is a bit of a task if you have tubby fingers. Accessing the interior involves pulling the body in two just above the outflow nozzle. In the top half, you’ll see the foam on the underside—the foam is finer than the Oase model so I’d expect more frequent clogging. On the bottom half you have an impeller cover with the flow control built in—simply pull that off and now you have the impeller. The Fluval model does have a lower power consumption than the Oase design (2.8W compared to 4.5W for the Oase), though in real terms that equates to a 30p saving per month based on electricity prices at the UK price cap (April ’24).
The Oase CrystalSkim comes with a 3-year warranty right off the bat, compared to Fluval’s 2, though at time of writing, my included Fluval paperwork does offer a third bonus year of warranty if the product is registered online within 30 days of purchase. So, it’s a pretty level playing field.
At the end of the day, both do pretty much the same job, and they do it well. And so ultimately it comes down to what you’re doing with them. If I’m trying to remove the protein film I get after every heavy feed in a messy cichlid set up (and I know the item’s going to get bashed by a moody oscar from time to time) then I’m going with the Fluval SK400. But if it’s to keep the surface immaculate in an OptiWhite aquascaping set-up replete with ADA canister filters and top-end glassware for pipework, the Oase is a no brainer.
Some of us in the hobby aren't always the biggest fans of surface skimmers. Arguably, some may feel that they could be avoiding a potential bigger issue and sweeping problems under the rug. Specifically, if there’s something in the tank that’s causing a film on the water’s surface, many would rather prevent it from happening, rather than jump in with something that avails the symptoms without addressing the root of the cause.
That said, in some cases the symptoms can in fact be the problem, especially where oxygen levels are concerned. Anything obstructing that delicate interface between water and air could spell big trouble for any livestock. These things have their place, for sure, but it's always advisable that if you’re getting regular films of gunk on top of your tank, you need to have a look at what’s causing it. Pro Practical Fishkeeping tip: most of the time it’ll be food related.
Related article: Finding the Right Protein Skimmer
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