Unboxed: Tunze 3155 Osmolator Auto Top-Up

The relatively high rate of evaporation from uncovered reef tanks often comes as something of a surprise to new hobbyists. Given that Salinity fluctuations resulting from this effect can have a negative impact on sensitive livestock, it quickly becomes clear that a reliable system needs to be put into place. Over the years we’ve used a variety of methods, from religiously trickling in RO water by hand daily to installing a peri-pump on a timer to drip Kalkwasser slowly overnight. Neither of these methods are ideal of course, indeed we’ve always longed to add a more accurate and less labour intensive option, in other words an automatic top-up (ATO).

Receiving a 3155 Osmolator top-up from Tunze was therefore most welcome. After some exhaustive internet research it was clear to us that this unit is a clear favourite amongst a large majority of advanced reef-keepers and reports of problems are few and far-between. Let’s comment on the packaging first of all, and as you might expect from Tunze, it doesn’t disappoint. Inside the box, individual components are packed tightly and cocooned safely in bubble wrap. Instructions are reasonably clear and a quick check of the component list reveals everything to be present and evidently undamaged. In terms of special features, this unit comes with powerful magnet holders that allow both the primary optical sensor and back-up float-switch to be securely positioned either on a sump, or directly on a display tank (it can also be integrated with Tunze filtration systems). Borrowed from the nano-stream range, the magnets are indeed very powerful so care is needed when handling them. In practice, they really do allow an unrivalled level of flexibility when it comes to positioning the sensors… there are no suction cups or unsightly brackets to fail here! Back to the optical sensor now, and this is what really makes the 3155 worth the money. Unlike float switches, this non-wearing component won’t jam and is extremely accurate, even in disturbed water, promising the detection of surface fluctuations of just millimetres (Tunze do recommend locating this sensor area where it will not be overgrown with algae, as this may interfere with the sensor). Controlling a small, energy-efficient pump the 5017 water level controller displays the unit status clearly through LED indicators, and also features an audible alarm. This unit can also be positioned easily with the Velcro strips supplied so you can see exactly what the system is doing. Able to service tanks of well over 100 UK gallons (and for larger tanks, there is an option to add a larger pump), it’s worth noting that the compact pump is also quiet and reliable.

At the time of writing this unit generally retails for around £140 which does make it one of the most expensive ATOs out there. However, couple Tunzes renowned customer service with the superior quality of the components though and we still think it’s a really good buy. Actually, we’d caution the use of cheaper units given the critical nature of this system.

Keep your eyes open for updates as we install this unit on our test tank. For those of you looking for a solution for smaller tanks (up to 200 litres) look out for the new Osmolator Nano 3152.00 which is due for released imminently. We are told this unit will feature a single float switch on a magnetic holder plus advanced electronics which allow for a timed delivery interval and cut-out to ensure that the unit never overfills.

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