Ok a few months ago I was plannig a DIY Ca reactor and realized that I really did not "need" it on the 75g. I though the whole setup was a lil more $$ than I thought (CO2, Reg, controller)
I started looking at
Kalk reactors... Hmm this looks easy I thought. So I ordered everything I need and plan the build this weekend.
On average 1g of supersaturated Kalk will raise the Ca by 25mg/l in a 40g system. Since I have roughly 90g total volume I figure I'll get 10-12 mg/l per 1g Kalk. This works out PERFECT for me since my Ca consumption is about 10mg/l per day and my evap is about 1.5g per day. It gives me a lil more room to grow.
I plan to start out with pure RO/DI during the day and Kalk overnight. I love timers

This will help me avoid and negative PH affects, but will probally have to go 100% kalk within 6 months.
I modeled tihs reactor after a few I saw online..
The materials
4" PVC toilet flange closed (base)
4.5" x 6" clear acrylic tube (for visual checking Kalk level)
4" PVC coupler (
recirc pump plumbed here)
24" 4" PVC (chamber)
3" rubber wing nut cap thinggy
MJ 400 for recirc
misc PVC and JG fittings.
Basically the flange will be the base followed by some acrylic. then a coupler. here I will install a in/out for the recirc and a 1/4" JG fitting for the RO/DI input. Then at the top of the unit I will install another 1/4" JG for the Kalk out to tank.
ATO hardware: (this is soo easy) credit to CRVZ
A simple 12vdc solenoid to controll RO/DI to the reactor.
2 float switches in series to controll solenoid
ac/dc 12v converter to power the soleniod.
WOW a automatic ATO for less than $40
one float at sump water lever and one float will be inverted at the top of the sump for overflow protection.
I will place the solenoid between the reactor and RO/DI unit and use a valve the throttle back the RO/DI pressure to about a 2g/day flow. since I have about 15g volume left in the sump and I dump skimmate every 2 days this will also protect from a overflow.
I will also install a check valve to prevent back siphioning.
My 1st step will be making the pump section... I will start that tonnight.
2 holes for the 1/2" pvc fittings and epoxy to hold them in and another hole for the JG fitting. I got a MJ 400 to start because its cheap and disposable but may upgrade to a MAG 2 is the MJ don't hold up..
More to come later and pics.....