(02/07/2009) - I like this unit. For a piece of equipment to be rated high it must be functional and very easy to use. Here's why this one is the best out there. 1- To fill it with a kalk slurry you first need to drain the equivalent amount. The side valve allows this. Very basic but important because taking the top off ever time is silly. Access cap is a clever design with readily available parts. 2- Large enough tube to produce clear or almost clear saturated kalk liquor. Easily keeps up with a 200 gallon system with a calcium reactor too. I do have very large corals too. 3- Notice increase purple algae with in a week on glass. 4- Powerhead is being abused but is easily replace. I have a pet peave about proprietary parts from Europe.

(04/22/2008) - i purchased both this and the 612 calcuim reactor package and i can't say enough about their high build quality and ease of assembly and operation. plug and play at its best.... highly recommended.

(03/24/2008) - This is my third GEO product and have to say that it lived up to the GEO standard. Set up was a breeze and the unit is built well. I can't find anything to comment negatively on with this reactor.

(11/07/2007) - I've been running this reactor for a few weeks now and love it! Excellent construction, very tight seals, awesome appearance. I did have a problem the second week of owning it though, where it would mix the lime all the way to the top of the reactor. I took it apart, and nothing seemed to be clogging it. It works fine now, and could have been an issue with the maxijet pump. The side valve comes in very handy for emptying the reactor also.

(10/09/2006) - Couldn't disagree more with previous reviewer. I had no problems at all with any leaks ( i used silicone lubricant on all o-rings, including the one on the maxijet)Followed the directions of only using a half cup of kalk at a time and have not had any problems so far with the pump. After a horrible experience with another brand, I can highly recommend the Geo.

(06/23/2006) - Bought this and the 612 Calcium reactor. Both are well made units, but, the o-ring seal is tough to achieve. You need to tighten the nylon screws almost to the breaking point to get it to seal. Bad design -- also bad routing of the o-ring grooves on both, as there are deep router scoring marks in what should be a very smooth surface...this is why the O-Ring will not seal. I made a full-surface sealing neoprene (closed cell) gasket for both units, and it fixed the problem. MaxiJet pump burns out easily -- have replaced mine twice so far, after only owning it for 2 months now. They clog easily and need constant maintenance, and, even with that, the impeller jams, and the pump goes kaput.