What effect does high alk (12-13dkh) have on corals?
 

I still have some Red Sea Coral Pro salt here and would like to use it but have had really high alk in the past. I have more frags now and my alk is used up faster so I thought I could switch back to Coral Pro but I'm a little hesitant. Did anyone here experience negative effects running high alk in mixed reefs?

Tanks that run with carbon dosing sometimes seem to have issues with alkalinity over 8 dKH or so, possibly due to low dissolved nutrient levels, although I've never seen any data to confirm the actual cause. You could try using the salt to see what happens, or use it in fairly small water changes and let the alkalinity drift back down before adding more of it. I would avoid a change of over 1 dKH in one shot for a tank with touchy stony corals.

IME, constancy in alk is a key for calciifying corals like sps and lps;so, I would avoid bouncing it around;certainly not more than 1 dkh per day. When corals grow skeletal matrix and tissue , the process involves a number of elements including alk , phosphate and others ; raising or dropping alk quickly can knock it all out of balance if the other elements don't match up.
Generally increased alk will encourage more growth from calcifying organisms in an environment balanced for it but may occassion stn and/or burnt tips in one where other nutrients are very low. My advice is to pick a number for alk in your tank between 7 and 11 dkh ( personally, I like 8.5 for my system) and then do your best to keep it steady.

I dose carbon and aim for 7.8-8.0 dKH. I would buy your salt to match, as closely as possible , the dKH you desire for you tank.

Here is a guide, a bit old but give a good idea.

I've a SPS tank, after a recent move I neglected my tank and one of my alk dosers went out of control. Tested last week and found my Alkalinity was 18.2dKh (yes, 18.2, not a typo).

I've been running my nutrients much higher to try and kick a dino outbreak, so I think that has been what helped prevent disaster. I've noticed growth has exploded (coraline especially, it went from a scattered assortment of pick dots to covering every possible spot in about two weeks).

25ppm NO3
0.63 PO4
18.2 dKH Alk
520 ppm Ca
1490 ppm Mg

Just checked my ALK kh 17 about don't know what happened pH is 8.4 gravity 1.24 ,0 amonia ,0 nitrites nitrates also just a tad over 0, phosphate little high installed a nitrites and nitrates and phos scrubbing pad in filters what should I do

To Reef Central

First, stop dosing any pH buffer or other alkalinity supplement. They all will increase the dKH. If the animals are doing well enough, then you likely can wait for the pH to drop.

What's the alkalinity of your freshly mixed saltwater, and the topoff water?