Alk and Mag questions


New member
So im a bit confused.

Most of what im reading says that you need to add equal parts ca and alk. Like a 2 part suplement like B-ionic (which i use).

I just recently had a large spike in alk bringing it up to over 13, however after a 30% water change a few days ago my Ca is 380 and my dkh is at 8.6. Id like to raise my Ca to around 420, but can i do this without raising my alkalinity at the same time?

I have a WM Calcium supplement i can add, but if i add it will it just precipitate out if i dont add some kind of alk supplement? Id like to keep my Alk where its at.

Also durring my testing i noticed that my Magnesium is at 1500ppm, and after doing some research i read that this can cause the tips of my sps to "burn" which some of mine are doing. I thought it was from the Alk spike but i think its because of the Mag being so high.

Is there anything i can do to bring it down? Keep in mind i did a 30% water change just a couple days ago and i havent added any type of Mag supplement for a couple weeks.

Ive been using the same salt for 3+ months and previous to adding a kalk reactor to the system (which has been disconnected for over a week, untill things get back in sync) i had a heck of a time even keeping it at 1200.

So i dont think its my salt mixture, i guess i can mix up a small batch and test it.

Randy Holmes-Farley

Reef Chemist
Premium Member
but can i do this without raising my alkalinity at the same time?

Sure. A onetime dose of the calcium part. Just let the alk decline before more alk dosing.

This has more:

An Improved Do-it-Yourself Two-Part Calcium and Alkalinity Supplement System

from it:

Dosing Instructions
The dosing instructions are basically the same for each recipe, although any given aquarium will end up using about twice as much of recipe #2 as recipe #1 to add the same amount of calcium and alkalinity.

To initiate dosing, first adjust calcium and alkalinity to roughly their correct ranges. This may require a substantial dose of just the calcium part if calcium is low (e.g., below 380 ppm). I would suggest targeting calcium between 380 and 450 ppm, and alkalinity between 2.5 and 4 meq/L (7-11 dKH; 125-200 ppm calcium carbonate equivalents).

This calculator shows how much of what parts to add in order to boost one or both of the parameters by a certain amount:
Reef chemicals calculator

Then, once things seem roughly correct, select a starting daily dose for routine dosing. Here are some suggested starting doses, but the exact values do not matter much. The suggested doses apply to both recipes.

After a few days of dosing, note whether alkalinity is low, high or on target. Only bother to test alkalinity, not calcium, during this period, because it is much more sensitive than calcium to over- or underdosing. Adjust the dose up or down as necessary to increase or decrease the alkalinity.

Once you have determined the proper dose, continue it until there is a substantial reason to adjust it (such as falling alkalinity as the corals increase in size). When adjusting the dose, raise or lower both of the recipe's parts together.

Resist the temptation to keep jiggering calcium and alkalinity independently. They will need occasional corrections, but that should not be the normal course of dosing unless there are substantial outside influences, such as water changes with a salt mix that does not match the tank's parameters or an error in making the mixes.

Check alkalinity fairly frequently to make sure the dosing continues at a suitable rate. Check it maybe once a week to once a month (or less as you get more experienced with the system and the tank). Check calcium once a month to once every few months to make sure it continues on track.

Remember to add an appropriate amount of Part 3 each time you finish adding a gallon of Parts 1 and 2.