Magnesium, Alkalinity and Calcium

[bwells]

My 125+30 gallon tanks have been operational since March. All of my systems work well and for the most part, things have been healthy and stable. My tank is very well stocked with about 20 fish, a dozen snails, crabs, shrimp and 10 different coral species.

Sometime in August, I got a flowerpot coral (about the size of a baseball) and a green birdsnest coral also about the size of a baseball. The birdsnest has never really looked like it is thriving. It has maintained its brown/green color, but the polyps seem to very rarely extend and that "fuzzy" look that it had in the LFS has never looked that way since I brought it home. The flowerpot coral for a few weeks after I brought it home extended a lot and was really full. But then it tended to also not seem to be thriving. All my other soft corals and my hammer coral all are very nice, always extended and full and brightly colored. All my fish and inverts also thrive and are colorful and healthy. I have the coral well spaced so no coral is within reach of another. The hammer is the only aggressive coral I have and it is on its own end of the tank.

So after several weeks of my birdsnest and flowerpot not thriving, I started reading everything I could find about possible causes. I tried moving the birdsnest into more flow and out of flow (a few weeks at a time in one location or the other). I also moved the birds next up higher in the tank to be closer to the LED lights and lower to be away from the LEDs. Since moving it down, there is a tad bit more green polyps showing. But it is still not happy. I keep the temperature at a steady 80F and I use an auto top-off system. I change 10% every week (I tried going to two weeks but it didn't seem to change anything).

So then I turned to chemistry. I only use tropic marin bio actif salt. I have read all I can on the balance of Magnesium, Alkalinity and Calcium. I got a reef foundation pro test kit and I began testing for Magnesium, Alkalinity and Calcium. I found my levels (with no additives) were lower than the target ranges of:



KH: 8-10 dkh
Mg: 1375-1450 ppm
Ca: 380 ppm


My first test of my water before additives was:


KH: 8.1dKH
Mg 1120 ppm
Ca: 315 ppm


Wise or not, I stated dosing with Seachem Reef Fusion 1 and 2 at a rate of 15ml twice each week. After just a few doses, I retested and found my levels were here:


KH: 9.0 dKH
Mg 1160 ppm
Ca: 420 ppm


I have basically maintained these levels and I felt I was on the right track. The Reef Fusion product does not explicitly mention raising Magnesium. And indeed my Mg levels never got above 1160. So I started dosing with Seachem Magnesium at a rate of 6 tsps twice a week. Yet, even after dosing at these levels, my magnesium once got to 1280, but then stayed under 1200. I tried dosing the magnesium once a day for a few days, and still when I tested, the levels were only 1220.

No matter what I did, I could not get my mg levels up to even the lower end of the recommend range. So just for kicks, I tried testing the concentrated mix before adding it to my tank in case my test kit was defective and as it should be, the levels were off the charts.

So over the past week, I noticed the flowerpot coral especially looking frail and my mushroom anemone has closed up to a large degree and is not eating very well. So I feared my mg levels may have gotten too high. I stopped dosing anything and did a 15% water change. Tonight, my flowerpot and anemone are looking somewhat better than they were; although still not thriving.

Here I am, seemly unable to get my magnesium levels up to even the lower end of the recommend range no matter how heavy I dose my tank. I am at a loss of what to do next. Should I completely stop dosing Magnesium, Alkalinity and Calcium? Should I just stop dosing Magnesium? Should I get a different Magnesium test kit? Should I just accept my flowerpot and birdsnest corals may not thrive, but they at least were alive and not looking too bad? Should I try dosing with some other system to raise and maintain Magnesium, Alkalinity and Calcium? Maybe Seachem 2 part system is not any good. I cannot afford an automatic dosing system for now.

What do you folks recommend I do next? I am totally open to try anything including just backing off all together and going back to my no-additive approach and just stop worrying about Magnesium, Alkalinity and Calcium.

But I do want more Coraline and I want my stony corals to thrive. I also have a couple of plants that like the calcium levels higher. At least with the Seachem 2 part system, the calcium and alkalinity levels were pretty good. But based on my reading, I may see calcium precipitate out of the water when it gets to the recommended level unless I also raise magnesium to the recommended level. as an aside, I never saw calcium precipitate from the water onto my heater for example. So maybe I don't need to worry about raising the mg levels.

Thank you for anything you can offer!

[bertoni]

Calcium at 315 ppm was rather low, but all the other numbers should be acceptable for your corals. You probably just need to dose more supplement to raise the magnesium level, although the 1100-1500 ppm range should be okay. This calculator might help:

http://reef.diesyst.com/chemcalc/chem_calc3.html

I'd target an initial dose of 50 ppm (if I decided to dose). The calculator requires a guess as to the actual water volume, so your results can vary quite a bit.

The SeaChem two-part should be fine. I suspect the problems lie elsewhere.

By flowerpot coral, do you mean a Goniopora sp of some sort?

[bwells]

based on pictures, my flowerpot coral appears to be Goniopora lobata. I will get a photo of both this and my green birdsnest coral tomorrow to share. Thanks for the calculator. Just roughly guessing at my tank being 100 gallons, this calculator says I would need like a pound of mg to get it up 100ppm. That's a LOT! I felt adding as much as I was adding was a lot, but based on this number, I was not even close to what I may need to raise it by 100ppm. With that in mind, it seems that my corals may not be negatively reacting to high mag after all. It says no more than 100 ppm per day. But 100ppm per day for my tank is like 1.0bs of mag per day. But it at least explains why adding what I did (6 tsps per day) was no where near enough to have a noticeable effect on the measurable levels.

[bertoni]

Yes, people often are surprised at how much supplement it takes to raise the magnesium level of the system. You can use epsom salts from the drugstore, if you'd like to save some money. That's basically all the SeaChem supplement is. There are DIY formula for more ionically-balanced supplements, too.

Does the Goniopora respond to feeding at all? Many species can take small prey.

[mindi]

I think from your post you are using the RedSea Pro Mg titration test..? If you read the RedSea sub forum here you will see many people having difficulty getting consistency from the test, me included. I must say that since watching their video tutorial and with more practice I think I have it sorted now. However it doesn't sound as though test consistency is your issue does it..? I use Red Sea coral pro and NSW water changes of about 20% month and my Mg fluctuates quite significantly between 1300 and 1500...it is my least stable parameter....and I still dont really understand why myself...my Ca is good around 420, Alk is 3.5meq/l....so Mg levels are a bit of a puzzle to me too.

[bwells]

I have been feeding the Goniopora a combination of daphnia and Cyclopeeze with a few brine shrimp using a syringe to target feed. I pass over all my coral with this mixture once a week. The Goniopora does not look too bad, but I use as my basis how it looked at the LFS and how it looked in the first week or two after bringing it home. At the start, the long polyps would extend really far and the tiny fingers on the end of those long polyps would seem to wave in the current and it would stay fully extended until my light went down to about 5%. Then it would close up tightly.

Now, it does not seem to extend as far anymore and the tiny finger polyps seem to just be hanging and not really waving. And it will sometimes close up more than once a day and start its final close-up a few hours before the light gets to 5%. But all of that said, it still opens up nicely and looks just okay; not spectacular like it did the first few weeks of having it. And the Seriatopora also just has not looked like it did when I first got it.

And this is what prompted me to to try the Ca, KH and Mg additives. Yes, I am using the RedSea Pro titration kits for all three tests. And I agree, it was not clear when the color change was complete. Based on the YouTube videos by Red Sea, they stop as soon as the color starts to change whereas I am inclined to wait until I see the color really be different. Either way, I have tested my Mg 3 times in a row just to see what I get and every time, I get the same value. So consistency seems to be good for me.

What other test kit do you like for Mg testing? I see Seachem has their own and I see the Salifert also has a Mg test kit. I also saw Seachem makes a Strontium supplement but I have not read much about supplementing with Strontium and I believe my Bio Actif salt includes Strontium anyway. I will post photos of my corals later today once they open up and get your opinion on what I am concerned about.

[bwells]

I just read an interesting article that has given me cause to pause... Many of you have probably read this already, but here is the link in case you have not:

http://web.archive.org/web/20030217103910/http://www.animalnetwork.com/fish2/aqfm/1999/apr/bio/default.asp

What is striking to me are these paragraphs:

The first “mysterious” cause of lower than expected magnesium concentrations in a reef aquarium is low overall salinity. Although I don’t advise running a reef system at lower than 35 ppt salinity, it isn’t uncommon for people to recommend running saltwater tanks at 30 ppt salinity or even less. If you use a synthetic seawater mix that perfectly emulates the ionic ratios in natural seawater, and only use enough of it to attain 30 ppt salinity, the magnesium concentration in your system will be only 0.0453 moles per kilogram or 1100 parts per million (ppm; w/w.) That is significantly lower than you might be expecting. The easiest way to correct this is simply to increase the salinity of the system to 35 ppt salinity.

Obviously, this doesn’t just affect magnesium. If your system is operating at lower than 35 ppt salinity, then it is likely that the concentrations of all major and minor ions is systematically low in your system. Aquarists should also be aware that all of the synthetic seawater mixes on the market have substantial water or hydration in them. In many cases, a “50-gallon bag” of synthetic seawater mix will make only 42 gallons of 35 ppt salinity synthetic seawater. (The mean salinity of the eight brands of synthetic seawater mixed to 35 grams per kilogram was 29.68 ppt, 50 x 29.68/35 = 42.4 gallons at 35 ppt salinity.)

I have my salinity at 32ppt. I have kept it at this level based on a recommendation from a LFS and from others I spoke to in the hobby. But now, with this article, it would explain why my Magnesium is staying around 1150 or so.

Just as an experiment, I am going to slowly raise my salinity to 35ppt and then see what my test kit registers for mg. Maybe my corals will be happier at the higher salinity. But again, the LFS I purchased my corals from keeps his tanks between 30-33ppt salinity.

What are your thoughts on salinity levels in your reef tanks?

[downbeach]

Here's an article worth a read:

http://reefkeeping.com/issues/2004-05/rhf/index.php

Here are four more articles worth reading:

http://reefkeeping.com/issues/2007-03/rhf/index.php
http://reefkeeping.com/issues/2007-04/rhf/index.php
http://reefkeeping.com/issues/2007-05/rhf/index.php
http://reefkeeping.com/issues/2007-09/rhf/index.php

[bertoni]

I agree that raising the salinity to 35 psu (or ppt) is a good idea.

I'm not sure why your coral is having problems. If it's still accepting food, that's encouraging, though. It might be reacting to a lighting change, I suppose, but that's beyond my area of expertise.