By Bob Goemans
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Osmotic Regulator

Manufactured by: Tunze

A product review by Bob Goemans

Product Review - Tunze Osmotic Regulator

(Written in 2001)

One of the most time consuming aquarium husbandry tasks is that of replenishing evaporated water. It's almost a daily chore where some aquariums are concerned. Too much evaporation without adequate replenishment will increase salinity levels and stress its inhabitants. And, adding too much makeup water at one time will only compound the stress situation. Fortunately, aquarium product companies have produced a wide array of devices called 'dosing equipment.'

Tunze recently announced its newest doser, or what is refer to as an 'Osmotic Regulator.' It provides constant water level control for the replenishment of evaporated water in either marine or freshwater aquariums. This new 'duel sensor' device, which is supplied as the "Osmolator Universal Model #3155," contains an infrared (IR) and float-type sensor. It is an upgrade of a previous model that used two float-type sensors. Its IR sensor, which has no moving parts and is unaffected by debris of any kind, now alleviates the possibility of any floating matter or calcium deposits from fowling the controlling water level sensor. The other sensor, a float-type sensor, when activated by a 'too high' water level, shuts off the DC power supply to the unit's metering pump. Since such a condition would be a rarity, float-type sensors are perfectly acceptable for this function. To tell you the truth, I never had a lot of ongoing faith in float-type sensors as the primary factor for controlling water level!

I want to thank Roger Vitko with AquaTek Tropical Fish (1) and Axel Tunze for sending me a unit to checkout. It comes complete with all mounting brackets/hardware/tubing, an all-electronic Controller with two sensors, a Metering Pump, Power Supply and a detailed Instruction Booklet.

Upon opening the unit's carton I first found a package containing two sensor holding brackets and a wide array of associated parts so they can be mounted to fit a variety of situations. In fact, the brackets can easily be mounted over the top edge of the aquarium/sump (feasible with glass aquariums since their top edge thickness is often quite narrow) or slid onto the usually wider horizontal inside edge lip of acrylic aquariums. In fact, both sensors can be mounted to a single bracket if desired, or separately, one on each bracket. Tunze has taken all mounting possibilities into consideration and supplied whatever associated parts would be needed. Very thoughtful of them!

The all-electronic Water Level Controller, #5017, has two Velcro self-adhesive strips on its back surface so it can easily be mounted wherever needed. It has four LED lights that have a variety of functions. If the Low Level Red LED is flashing, the container with the makeup water is either low and/or the metering pump has ran for more than 10 minutes signaling something else has intervened and not enough water has been supplied in those ten minutes to make up for what has evaporated. A Yellow LED operates when the metering pump is delivering water. I should note the pump operates for a minimum of about 10 seconds to prevent frequent switching operations since the IR sensor is so accurate, e.g., keeps water level to within one millimeter. The Green LED is lit when the water level control IR sensor is in contact with water, signaling the water level is at its predetermined level. When the IR sensor doesn't contact water for three seconds, a signal is sent to the pump to begin pumping. There's also a Red 'Too High' LED, which is activated by the Too High float-type sensor. If activated, it turns off the pump and also sounds an alarm, which is built into the Controller. The alarm can be disabled if desired by opening the controller and following the directions in the unit's instruction booklet. Should both Red LED's be activated at the same time, moisture has somehow gotten inside the controller and all functions have been switched off until the problem is resolved. Resetting it simply requires electrical power to be turned off, then back on.

The small three inch high, but powerful metering pump comes complete with about ten feet of black tubing. A supplied DC power adapter powers it. When the unit arrived I was pleasantly surprised by the array of mounting possibilities for the sensors. It was not first necessary to jury-rig some sort of holding device for the sensors. Since my plenum sump tank is acrylic it has a wide lip around its upper level. Having this possibility already taken into consideration in the design of this product's possible mounting situations made mounting the sensors a snap! For this test review I mounted the IR sensor on one bracket so it just touched the desired water level in the sump tank. The 'Too High' float-type sensor was mounted a few inches above the IR sensor, on the same bracket. The very detailed instruction booklet explains a variety of possible set-ups.

The Water Level Controller was then mounted on the front face of sump tank. One end of the black water supply tube was pushed into its mating socket on the top of the metering pump and the pump lowered into a nearby reservoir tank. The other end of the supply tubing was connected to a supplied clamp that either locates to the top of the mounting bracket or the top edge of the tank. This assures the outlet of the water supply will not go anywhere other than where it should! Another thoughtful idea incorporated into its design. The power supply was switched to 9V, as it can be set to a wide variety of DC voltages, and its power supply cable inserted into the base of the Controller. Everything was double-checked and the power supply was inserted into an electric outlet.

The metering pump made some noise, but did not flow water until I primed it by sucking on the end of the supply tube. I understand if I would have tilted the metering pump somewhat the air blockage in the pump would have been released and it would have started without the sucking method. Force of habit where aquarists are concerned I guess! The pump ran and ran and even though water now filled the sump beyond the IR sensor, the pump did not shut-off. I lifted the float ring on the Too High sensor and the Controller's alarm sounded and the pump was shut off. Nice to know the emergency shut-off works well! When I released the float ring, the alarm stopped sounding and the pump again began operating. This time I shut off the power supply. After re-reading all the instructions I could not find anything needing correction, so I turned the power back on for another go-around. No pump operation this time, so I moved the IR sensor very slightly out of the water and the pump began operating. I dropped the IR sensor back into the water and the pump, after running for about for 10 seconds, shut off. I tried moving the IR sensor to various heights above the water level and each time water came in contact with it, the metering pump shut off. It now appeared to be working perfectly! Could be the circuitry simply needed resetting.

With my schedules, my aquarium would not survive without dosing equipment. Being able to replenish exactly what is being used provides for an extremely stable environment salinity-wise, and that's exactly what the new Tunze water level controller accomplishes. And, all with the assurance it is a fail-safe device and needs no maintenance. The product has a twelve-month guarantee, and I can attest to the quality of Tunze equipment as I have used and still use some of their products. They have been in business for over 40 years and are a well-respected company worldwide. This unit can also be used with other Tunze products such as the Osmolator 5002, the Osmomat 5024, and the Comline quick-run filters.


1) AquaTek Tropical Fish, 8023 Burnet Road, Austin, TX 78757, (512) 450-0182, fax (512) 407-8273,

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