question on calcium, magnesium alkalinity relationship

[creatureteacher]

I have a 36g corner bow with a lot of SPS corals. It is doing well and the corals are growing so fast that you can almost see daily changes. Due to the volume of the tank and the fact that I don't have room for a calcium reactor, I decided when I started the tank to use a 2 part calcium addative. My problem is that I have so many corals, I am adding 60ml each of the two part daily. I try to keep my alk at 11, but it drops to 7 by the following morning. I can't believe this swing can be good for the tank, but I haven't seen any stress on the corals. I have two questions: is there another addative I could use that might keep the alk and Ca up so I wouldn't have to dose daily? My other concern is my magnesium. It never seems to drop. It seems to stay at 1260-1300 all the time. I have tested it with several different kits and it stays put. Why? Is there enough magnesium in the Ca solution to compensate for the metabolism of the corals, or don't they use that much Magnesium. Any help would be greatly appreciated.

 

[stingythingy45]

Your alk should not be droping that fast over night.I would look into testing that with 2 different kits.
Mg. typically drops very slowly.If you are doing water changes with a good quality"Reef"salt this will help supplement that parameter as well.
What's your calcium?

 

[pvh]

I used to see my alk drop by that much. To solve this you could use a doser for both alk and ca.

Mag don't fluctuate as much as the other two but you should check on it at least once a week if your alk is dropping that much.

I use a doser that can dose all three.

 

[AnthonyP]

Mag levels help keep Alk and Calcium in check - ideally if your mag is at 1300 you want the calcium at 430 or so and Alk prob mid to high 8's or low 9's

I have some questions hopefully could help find the solution....
do you have a PH probe? or monitor PH?
what salt do you use?
Which 2 part recipe do use?
Which test Kits have you tried?

 

[delta]

If you are dosing larger amounts you may need to start dosing a few times a day or start topping off with buffered RODI or kalk water & dosing.
But always get a second opinion/set of eyes on things like this if it is all of a sudden and you have no indication from you corals something has changed.

Your Mg is a bit low and that can aid in dropping you Alk, try bumping Mg up to 1350-1400.

If your Ca and Mg are are the low side say CA 400 Mg1260 your Alk is not going to stay 11dkh as the other two are driving it down.

Personally I feel 11DKH is high to run a reef tank as one of the worse things you can do is bounce your ALK. If you alk is 8DKh and something goes wrong it won't plummet like it will at 11DKH
so if you go from 8-7 then back to 8 instead of 11-7 and back to 11, you stand a better chance of not seeing the effects of a serious Alk swing

IMO if you are needing to dose larger amounts you are at the point you need a calcium reactor. Big investment up front but a solid move anyone keeping a lot of SPS.

 

[creatureteacher]

Your alk should not be droping that fast over night.I would look into testing that with 2 different kits.
Mg. typically drops very slowly.If you are doing water changes with a good quality"Reef"salt this will help supplement that parameter as well.
What's your calcium?

I've tested with two kits and get the same results. I have the same issue with my calcium. It will drop from 450 to 400 overnight.

 

[dcforester1]

Im glad to see this post. I have been battling with my Alk for the last couple of months. I was wondering if someone could explain what the relationship should be between the two?

I cannot get my alk to stay up at 8. My calc is at 460, and my Mag is a 1350, I am using a reactor but it will not stay up. I have a heavily dominated SPS tank with six clams, and I am wondering if that is the problem. It might be time for a bigger reactor, I don't know. I am adding about 8oz of alk every other day.

I was reading at the reef calculator website it states your alk should be at ??? when your cal is at ??? so i was wondering if I have my levels off?? Basically if you alk is at 8 is there a number that your calc should be at?


TIA Derek

 

[delta]

Around 400

 

[dz6t]

Do you see Cal swing along with Alk swing?
If you do, it means you need a much bigger water volumn to support your SPS stock as it is.

 

[dcforester1]

Do you see Cal swing along with Alk swing?
If you do, it means you need a much bigger water volumn to support your SPS stock as it is.

No I am only seeing an alk swing. Sorry creature i didn't mean to highjack thread. So if my calc is at 460 what should the alk be at? and how do you know what the two should be at? is there a formula, or chart/scale??


TIA

 

[dz6t]

Please note that most of the test kits are not very accurate. IMO, you want to keep stable parameters instead of shoot for a set value. There is only so much cal and alk a given volumn of water can hold. Increasing water volumn will be a solution (or reduce the among of SPS in the tank).

 

[creatureteacher]

Please note that most of the test kits are not very accurate. IMO, you want to keep stable parameters instead of shoot for a set value. There is only so much cal and alk a given volumn of water can hold. Increasing water volumn will be a solution (or reduce the among of SPS in the tank).

This doesn't make sense. You can have a Kh of 10 and 450mg/l of cal in 10 gallons or 100 gallons, so how does the volume affect this?

 

[Cjtabares]

Please note that most of the test kits are not very accurate. IMO, you want to keep stable parameters instead of shoot for a set value. There is only so much cal and alk a given volumn of water can hold. Increasing water volumn will be a solution (or reduce the among of SPS in the tank).

This doesn't make sense. You can have a Kh of 10 and 450mg/l of cal in 10 gallons or 100 gallons, so how does the volume affect this?

If u have 450 mg/l in 10 L you would have 4500 mg of cal if you had the same 450 mg/l in 100 L you would have 45000 mg of cal. If your coral,in both volumes, use the same amount of cal it will take longer to use the cal in the 100 L volume. I would think.

 

[The Ng Thing]

I was wondering if someone could explain what the relationship should be between the two

I'm curious as well. My tank was fine for a while and within the past couple months I've been struggling with this same issue to the point where my SPS are starting to recede.

 

[creatureteacher]

If u have 450 mg/l in 10 L you would have 4500 mg of cal if you had the same 450 mg/l in 100 L you would have 45000 mg of cal. If your coral,in both volumes, use the same amount of cal it will take longer to use the cal in the 100 L volume. I would think.[/QUOT

I understand what you are saying. Obviously it would take longer for the corals to use the available Ca, Alk and Mg in a larger volume of water, however, this just means you would have to ramp up your dosing to meet the demand in a smaller volume of water. The statement was a bit confusing as it was implied that a smaller volume could not hold the same mg/l.