struggling Mag Levels

[Mzj7725]

My corals are beginning to struggle. I am fairly new to corals (3 months in) and only 15 months into reefing. I have hammerhead, 2 frogspawn, trumpet coral, duncan, birds nest, GSP. Hammerhead and frogspawn are doing the worst

75 Gallon with 30 gallon fuge

Mag - 990
DKh - 8.9
Calcium - 380
Nitrite nitrate ammonia - 0
PH - 8.2
1.024 salinity
Temp - 78.2

I use instant ocean reef crystals and do 7.5% water changes weekly

I know Mag is supposed to be up to 1300. First question is why is it low and second question is how do i get it back where it needs to be.

THanks

 

[organism]

It is much, much easier for you to use the search function on this site to get all of that info since there's quite a bit to it and you need to be pretty educated on how the big three calcium/alkalinity/magnesium work in order to have a thriving tank. I'm surprised that 15 months into reefing and 3 months into a coral tank this has just now come up, but it's going to be a great learning opportunity for you

 

[Mr tap water]

Have you tested your meg in your salt water mix before adding it to your system if it's a lot lower than what it suggested on the brand of salt I would suggest trying a different brand and if it matches Buy yourself some magnesium and just keep topping up gradually until you reach the required level ,
you need to be aware magnesium can drop on a daily basis just like your KH and calcium.

 

[Reef Frog]

The explanation could be low levels in the salt mix or usage I suppose.

I use the dry magnesium supplement by Seachem called Advantage. It is designed to be mixed in RODI water and added to the tank. There are many other brands available too. There are also DIY options that will save you a little money from supermarket sources. There are detailed threads on this written by chemist Randy Holmes Farley in the Chemistry Forum on that subject. it also covers proper dosing and has numerous options on the other elements as well.

Whichever you use, you'll probably be surprised at the high volume of material it takes to get it up even 100 ppm. So don't buy the little bottles!

Raising it to 1300 ppm by adding 100 ppm per day is safe. Be sure to use the simple reef calculator made by Dr Homes-Farley and it will guide you on how to use the Advantage and several other products; how much to add to get your level up and how much to keep it there. Magnesium usually is depleted slowly so most people don't use an automated dosing pump to administer Mg. It is usually enough to dose it fairly infrequently by hand.