Hi Sam,
The box has a tiny pump that circulates the water in the overflow box only. It has something to do with providing a better level and contact with the sensor.
Or something like that.
Its not the dosing pump that sits in the refill water.
The pump cannot drive any of the larger kalk reactors. Just not made for it, although it can pump up to 9 feet. Its a 12v pump, so in order to use any 120 pump the switched socket I mentioned, is needed. The 12v system is supposed to be safer.
The optical sensor, reacts to the slightest drop in water. If you removed a cupful it would pump it back. Also has a back-up mechanical float switch to shut it down if something fails, plus warning lights and alarms for high level.
They say the pump should last for a few years and is only $18 US to replace. If it pumps kalk, without the dispensor, {straight from the tub, then its life may be reduced considerably.}
The kalk dispensor @ $120 Canadian, is pretty pricy,{IMO}. But I guess its to do with the Tunze name and German tech. Its does work well and should easily keep up to a 38 gal tanks demand. Its sits in a 5g saltwater bucket thats full of refill water. You throw a couple of tablespoons of kalk in the dispensor when you fill the water bucket up. The pump pushes the water into a tube near the bottom of the dispensor. This agitates the kalk, keeping it mixed somewhat, but only clear kalk water exits the top, back top the tank. Because its small, {about the size of a 2 litre pop bottle}, compared with my 3ft by 6in. kalk reactor, it can only handle so much kalk at once, which is what limits its top end capacity.
Of course you could just use top-off water and drip kalk or whatever your using now, but I think the extra $120 for the dispensor for a tank your size, may be worth it. Depending on evaporation, this would at least give you the amount of time a 5 gal. bucket of top-off water would last.
Someone looking after your tank, just needs to throw a couple of spoons of kalk powder into the dispensor and refill the bucket with fresh water. {we use the large Instant Ocean salt buckets.}
From Rodger Vitko on the Tunze forum at RC. The overflow box is 2in. deep by 4in. long by 5in. tall. If you have plastic trim on the tank, then you require part #3000.244, which is a longer set of mounting screws and a suction cup.
Another friend order this for his,
Osmomat #5024
Kalk dispensor #5074.000
Screw/holder set #3000.244
I hope this babbling is of some use to you.
Some is from my experience, most from the Tunze forum. Take it for what its worth.
I can tell you my friend would not trade his for nothing. As for me, well I am a confused person.
If I could decide on keeping my sump or not, I could decide which unit to run. The Osmolator is not very good for in tank use, unless the water level is down several inches. My scrubber and skimmer run direct from the tank, so I keep playing with sumpless.
I currently top-off manually, which is part of the reason I cant come out for a visit.
I do have an electronic float switch on my sump. Also when running sumpless, my scrubber pulls a gallon of water from the tank to feed the dump tray, playing havoc with any top-off. I am working on that problem. I can say for certain, I will use either an Osmolator or Osmomat , once I decide. They are that impressive.