Magnesium dosing, pumps jamming, and sand bed cementing

pfoxgrover · Jan 24, 2017

For many years I have been two part dosing BRS 2 part with dosing pumps running once per hour on a twenty four hour cycle separated by 30 minutes. I have a 240 gallon display tank with a mixed reef with mostly SPS and 2 clams, one medium sized and the other pretty large.
To keep Ca and Alk levels stable I am dosing approx 432 ml Calcium and approx 460 ml Alk (soda ash) per day. I also use a a kalk reactor with my ATO unit.

To supplement Magnesium I usually wait till it gets low (like 1200 ppm) and try to drip dose it near my overflow intake with a gravity fed gallon container over a day or so like 1 drip every three seconds of BRS Mag solution (7 cups Mg chloride and 1 cup mag sulfate per gallon of Mag solution).

I have been having a prolonged precipitate problems with freezing pumps and hardening substrate. When I have been trying to up my Mag levels to 1300 - 1350 to prevent precipitate from forming on pump bearings and in the sandbed, it seems to have the opposite effect as over time I have linked these pump freezing events to when I dose magnesium.
To try to help this I tried just a adding about a quart of BRS Mag solution to by weekly 20 ish gallon water change water and allowing it to mix with the new seawater for a few days.
This weekend I noticed that this wasn't raising my magnesium levels much at all so I tried putting 1 quart of Mag solution in about 3 quarts of new seawater(instant ocean at 35 ppt) and started a slow drip.

When I got home today 3 of my four powerheads were froze up!

How can I minimize my precipitate problem?
Is my idea to supercharge my water change sea water with super high Mag levels the best way to boost Mag levels without turning my tank into cement?
Is it weird that dosing Mag Solution with a slow drip seems to freeze my pumps almost like clockwork?
Any help is appreciated!

Current levels:
Alk 11.5 (usually shoot for 9 to 11.5)
Calcium 480 ( targeting 420 to 450, just reduced dosing a bit)
Mag 1200 (targeting about 1300 - 1350)

Reefing Madness · Jan 25, 2017

@Randy Holmes-Farley

Randy Holmes-Farley · Jan 25, 2017

There shouldn't be increased precipitation from magnesium dosing.

What exactly are you using? You certain it can't be mislabeled?

Randy Holmes-Farley · Jan 25, 2017

"This weekend I noticed that this wasn't raising my magnesium levels much at all so I tried putting 1 quart of Mag solution in about 3 quarts of new seawater(instant ocean at 35 ppt) and started a slow drip."

That is not a good idea. That could precipitate magnesium hydroxide and/or carbonate.

Randy Holmes-Farley · Jan 25, 2017

Either magnesium chloride or magnesium sulfate or both dissolved in fresh water and dosed to the aquarium to any reasonable levels won't increase precipitation.

pfoxgrover · Jan 25, 2017

Randy,
Thanks for the reply. I will stop trying to dilute mag solution in sea water. I had an idea that was not a good solution but I was getting desperate and tried it without doing my research.
My powerheads are very susceptible to freezing up and there really appears to be be a correlation with my mag dosing and participate problens. I understand that should not be the case so there must be something else going on.
I don't believe the products are labeled incorrectly. Maybe I should just dilute the solution with a lot of fresh water?

Randy Holmes-Farley · Jan 25, 2017

pfoxgrover said:
Randy,
Thanks for the reply. I will stop trying to dilute mag solution in sea water. I had an idea that was not a good solution but I was getting desperate and tried it without doing my research.
My powerheads are very susceptible to freezing up and there really appears to be be a correlation with my mag dosing and participate problens. I understand that should not be the case so there must be something else going on.
I don't believe the products are labeled incorrectly. Maybe I should just dilute the solution with a lot of fresh water?

What solution is it, and does it get into a pump before it mixes into the tank water reasonably well?

pfoxgrover · Jan 25, 2017

Randy Holmes-Farley said:
What solution is it, and does it get into a pump before it mixes into the tank water reasonably well?

The solution is 7 cups Mg chloride and 1 cup mag sulfate mixed in one gallon RODI water. It should get mixed really well before getting to the powerheads.
Do you think diluting the Mg in more RODI water would help? It gets mixed well in the tank before it gets to the powerheads.

Randy Holmes-Farley · Jan 25, 2017

I can't see more dilution helping since I can't see how you are getting precipitation.

I'm worried that you cannot see a rise in magnesium. Perhaps it is just testing error, or you are not adding enough to detect, but magnesium cannot ever just precipitate by itself. At the very least, it takes out massive amounts of alkalinity in doing so. To drop 100 ppm of magnesium takes more than 20 dKH of alk to be removed.

Randy Holmes-Farley · Jan 25, 2017

A gallon of my recipe (as BRS sells) should boost magnesium by about 200 ppm in 240 gallons of water.

pfoxgrover · Jan 25, 2017

With respect to my comment that I was having a problem with raising my Mg levels, I think you probably already solved that. My idea of spiking my weekly water change water with Magnesium was when I was seeing poor results raising Mg levels.

I generally have not have had a problem raising the levels. I have changed my test kit not that long ago and I have new reagents I can try as well.

I think maybe where I am struggling is when I try to catch up on Mg levels after maybe a month or two with no additions and when I try to ramp the levels back up over a few days or weeks, that is when I seem to be having the precipitation problems.
I could try again with weekly dosing of Mg.

I am dosing close to a half liter per day of each 2 Part per day (about 3150 ml per week each), and using kalk for top off water.
Roughly, about how much BRS Mg solution should I be adding each week to keep Mg levels up?

Randy Holmes-Farley · Jan 25, 2017

With my DIY two part, it is 610 mL magnesium part per gallon of alk part.

For limewater, the balanced amount is about 6 mL of the magnesium solution for each gallon of limewater added.