[Delphinus]

If it isn't too late, you might want to consider enrolling in the calcium reactor design course currently being offered over at reefs.org. I looked that at course and was seriously tempted, I still am, I just don't remember when it was running again (I think it was later ... the other courses should be well under way by now?)

Using non-reactor-media-grade sand has other potential problems besides the non uniformity of the grain size, such as leaching of excessive phosphates into the tank. Or was that if you use oyster shells, I really don't remember.

Anyways for the cost of ARM, you're not really saving anything by avoiding it. If you have the excess sand and want to go to an upwards flow reactor, then heck, give it a try. I went with sand first because I wanted to see what would happen. It did work OK from the point of view it affected my Alk and Ca levels, but my reactor was tooooooo big for what I trying to do with it, way too tall a column of sand to try to push water through it (maybe if it was less than 12" it would have worked, or if maybe if there wasn't that extra chamber on the bottom). But like I said, $25 for a package of ARM isn't really a huge impediment. Espescially considering the cost of everything else. Acrylic, CO2, cylinder, regulator, solenoid valve, etc.

I don't know about the upwards flow versus downwards flow. Were I to build another, I'd do the upwards flow but only because I just want to see what difference it makes.

I have the downwards flow right now, and my Alk and Ca are fine. So it's not like a downwards flow is somehow inadequate.

As far as dual chamber designs ..... personally, my take on it is this: The theory behind them was that they were a good idea to use up more CO2 before returning the effluent to the tank. In reality .... it almost seems as if it was more of a fad than anything else ... last year (2001 timeframe) it seemed as if everyone was going dual chambers, nowadays I see less of it. I think .... it's a great idea if you want to have more media, and space is a concern. Personally I like a larger single chamber but that's me.

Height ... well, looking back, I dont think I needed anywhere near as large a reactor that I built. I look at the ones you can buy and reactors half the size of mine are rated for tanks 5 to 6 times larger the size of my tank. So there's some food for thought. I went big because I wanted big. But for no reason in particular. I'm sure a 18" tall reactor 4" diameter would have worked fine, too. WOuld have been cheaper to build, as well. Oh well.

Square versus round tube ..... go with whatever works for you. I like tubing, but square works fine too...

Anyways there are my thoughts... hope some of them are useful