Tunze Osmilator 3155 or 3152?

[SynDen]

Going to purchase an ATO system soon and doing a bit of research on them. I would like a tunze but the price tag is hard to swallow for the 3155 regular system. They do offer a 3152 nano version however that is about 100 cheaper then the 3155. Since this is going in my 20g sump I am wondering if I can get away with putting the nano version in? What is the real difference between the two?

 

[Munch]

I had both, the 3155 runs with the optical. You can get buy with the nano if looking to save. Or find a gently used 3155 like I have on mine

 

[jahmic]

I have the 3152 and am happy with it.

The more expensive model uses the optical eye as the primary switch for the ATO, and has a float valve for a fail-safe IIRC. The 3152 uses just the float switch, and the fail-safe for the unit in case the float valve sticks on is that it limits the pump's runtime. The downside is that if you will have to manually reset the unit by cutting power to it for your ATO to start working again.

I haven't had any issues with my 3152 sticking on. In fact, when I get lazy and the float switch needs cleaning, it typically gets stuck sitting up when the water level drops, so the ATO doesn't turn on when it should. I've gotten in the habit of just cleaning it monthly and haven't had any issues.

 

[SynDen]

Ah so it is the optical switch that is the difference, good to know. I can see where that would be useful but I wont have trouble keeping the float switch clean on the the 3152 as I clean all the equipment in the sump once a month anyway. So looks like a 3152 for me, unless as Munch mentioned I can manage to find a 3155 that is gently used for a reasonable price, but havent seen any of those pop up recently.