Kalk would be perfect for you.
And cheap, at 5.00 for two pounds of Mrs. Wages' Pickling Lime.
To use: do you have an autotopoff system? If you don't, get one. You'll need a topoff unit: mine is from autotopoff.com, dual float switch in-sump unit. You'll need a maxijet 1200. You'll need whatever bucket you're using for topoff, but it must be ro/di water and it must have a lid. You have to use ro/di for sps anyway, so if you don't have your own filter, get one.
Now, after your topoff is running, insert a locline 1/4" plug in the end of the maxijet's hose: use a hose clamp or glue to make it stay put. Attach locline 1/4 inch to run to wherever your want the topoff to enter your system, and firmly brace/clamp the end of it. 5 gallons of kalkwasser in your carpet is messy beyond easy explanation.
Dump somewhat over 2 tsp of kalk powder per gallon into topoff bucket, stir. Use sponge gasket on rim to lid bucket tightly, with locline exiting and topoff pump in bucket...propped up OUT of the white muck in the bottom of the bucket: don't suck up that stuff. As you add more ro/di that gunk will dissolve eventually.
It will use your tank's evaporation to put in dissolved kalk via your ro/di topoff, and will HOLD whatever alk/cal reading you started with. So set that by dosing. The only thing that will make it fall is: slowing of evaporation; running out of water in topoff bucket; or running out of magnesium in your system.
Easy, cheap, saves a bundle, no extra equipment. My topoff bucket is 32g, so I dump in a half a pound of kalk and forget it for a week. Test once a week, and of course observe your corals.
The stuff is safe: I've twice goofed and shot my tank full of white---all specimens lived, no problem. Immediately check your ph and your salinity (kalk IS fresh water)---fix ph with mild doses of bar soda water, correct salinity. All ok. Fresh water overdose is as big a problem as ph rise: correct both...but remember the ph will self-adjust with kalk very fast, so don't correct unless really big ph swing (big,big,big overdose).