Why does my tank seem to use lots of magnesium, a little alkalinity, and no calcium?

[Koty]

Your issues fall between the fact that your Mg and salinity tests may be inaccurate, leading you to elevated Mg consumption.
Also, according to your post, you are doing everything the wrong way or, to say nicely, unconventional:

I rarely do any water changes
I dose 10 ml of phosphates daily
I dose about a teaspoon of sodium bicarbonate every other week
I dose 20 ppm of magnesium every other day.
My top-off water is tap water.

Besides your Mg consumption, is there any problem with corals or other tank inhabitants? If not, maybe you found a new dosing method. Where I live, I better use urine to top off rather than use tap water that is very hard and full of Chlorine and Chloramins.

Finally, "2 Halichoeres wrasses"? Once they become two males, one will end up dead.

 

[Jason_MrFrags]

Test your tap water and see what your actually adding to your tank. Consider getting a RODI.

 

[peterhos]

A little background:

I have a 125 mixed reef tank with a 40 gallon sump - I estimate about 100 gallons of water after subtracting the rock and sand displacement and my dosing estimates are pretty close to accurate based on dosing for 100 gallons.

The majority of my corals are still frags and are slowly becoming small colonies. It's stocked fairly decent with fish but not over stocked - 2 Tangs, 2 Damsels, 2 algae Blennies, 2 Halichoeres wrasses, 3 clowns, and 5 Cardinals.

Now, the interesting part:

I rarely do any water changes, I dose 10 ml of phosphates daily, nitrates are up and I'm working on lowering those, calcium stays around 480, I dose about a teaspoon of sodium bicarbonate every other week, and I dose 20 ppm of magnesium every other day.

I'm guessing part of my "issue" could be that my top off water is tap water (I know...) And that it's probably high in calcium and it definitely has alkalinity (I think 7.8 dKh) so I'm technically dosing alkalinity there and probably calcium as well.

Lately though, I'm having really aggressive growth on Cyphastreas and Acros and I still am not seeing a drop.

July 4th to today:

May 29th to July 4th to today:

May 29th to today:.

No before pics but I just moved this 2 weeks ago and it's already encrusting the glass:

Again, no progress pics but both have expanded upwards and downwards by almost 1" in the last 2-3 weeks:

I'd say my tank is not suffering so the calcium must be coming in through the top off water?

A little background:

I have a 125 mixed reef tank with a 40 gallon sump - I estimate about 100 gallons of water after subtracting the rock and sand displacement and my dosing estimates are pretty close to accurate based on dosing for 100 gallons.

The majority of my corals are still frags and are slowly becoming small colonies. It's stocked fairly decent with fish but not over stocked - 2 Tangs, 2 Damsels, 2 algae Blennies, 2 Halichoeres wrasses, 3 clowns, and 5 Cardinals.

Now, the interesting part:

I rarely do any water changes, I dose 10 ml of phosphates daily, nitrates are up and I'm working on lowering those, calcium stays around 480, I dose about a teaspoon of sodium bicarbonate every other week, and I dose 20 ppm of magnesium every other day.

I'm guessing part of my "issue" could be that my top off water is tap water (I know...) And that it's probably high in calcium and it definitely has alkalinity (I think 7.8 dKh) so I'm technically dosing alkalinity there and probably calcium as well.

Lately though, I'm having really aggressive growth on Cyphastreas and Acros and I still am not seeing a drop.

July 4th to today:

May 29th to July 4th to today:

May 29th to today:.

No before pics but I just moved this 2 weeks ago and it's already encrusting the glass:

Again, no progress pics but both have expanded upwards and downwards by almost 1" in the last 2-3 weeks:

I'd say my tank is not suffering so the calcium must be coming in through the top of water?

For a couple of years before redecorating I used tap water for top up and water changes. I live in a hard water area on the edge of London. For those 2 years the softies grew like mad and the tank had no obvious problems. I wonder what would happen if I went back to tap water (which presumably is of good quality around London)

 

[Aquariumaddictuk]

For a couple of years before redecorating I used tap water for top up and water changes. I live in a hard water area on the edge of London. For those 2 years the softies grew like mad and the tank had no obvious problems. I wonder what would happen if I went back to tap water (which presumably is of good quality around London)

If it's anything like the water in Cambridgeshire-its harder than Chuck Norris & around 40ppm of nitrate.
I won't even drink it let alone keep my discus or corals in it

 

[Icryhard]

Magnesium is only depleted at 1/10th the rate of alk and calcium depletion.

I thought the ratio was 3 to 1 with magnesium and calcium in respective order?

 

[Lavey29]

I thought the ratio was 3 to 1 with magnesium and calcium in respective order?

That's not my understanding and my tank is not 3 to 1 ratio for mag either. Search some of Randy's responses to mag consumption and you will see he references 1/10th ratio but of course this is a general guideline.

 

[tbrown]

What are you topping off with?

Tap water. I know, I need to get an RODI.

Our water has high alkalinity and calcium.

 

[tbrown]

Finally, "2 Halichoeres wrasses"? Once they become two males, one will end up dead.

They're different breeds of Halichoeres. Leucoxanthus and Melanurus.

Besides your Mg consumption, is there any problem with corals or other tank inhabitants? If not, maybe you found a new dosing method.

My corals are happy and growing. My fish are happy and eating. Out all day swimming around and interacting. My snails are breeding.

 

[Koty]

They're different breeds of Halichoeres. Leucoxanthus and Melanurus.

OK, that's not a problem. I had Melanorous and Vrolick's. After about 6 months they started fighting to death. I had to wait for Vrolick's to almost die so that I could take him out and save him.

 

[Icryhard]

That's not my understanding and my tank is not 3 to 1 ratio for mag either. Search some of Randy's responses to mag consumption and you will see he references 1/10th ratio but of course this is a general guideline.

If so I'd honestly like to see some sources. Not questioning whether he's actively trying to spread misinformation, but when I basically read everywhere that it's a 3 v 1 ratio you sure do need some good evidence to support such claim... but in regards to your tank: How much is your calcium / magnesium? I am guessing your magnesium is roughly 3 times more than your calcium, not?

 

[Lavey29]

If so I'd honestly like to see some sources. Not questioning whether he's actively trying to spread misinformation, but when I basically read everywhere that it's a 3 v 1 ratio you sure do need some good evidence to support such claim... but in regards to your tank: How much is your calcium / magnesium? I am guessing your magnesium is roughly 3 times more than your calcium, not?

Alk 8.4. Cal 470 and mag 1450 per ICP test 2 weeks ago and my weekly testing. I dose 35ml of alk and 35ml of cal daily via ESV 2 part. I add 15ml of mag weekly in-between water changes only not on water change week.

Post from Randy few years back:

Real magnesium consumption is more like 0-2 ppm per day, and cannot be much higher. It really can't be much more than 1/10th of the calcium drop rate.

 

[Randy Holmes-Farley]

I thought the ratio was 3 to 1 with magnesium and calcium in respective order?

A typical ratio is


17.5 mg calcium
1.5 mg magnesium
30 mg = 1 meq/L = 2.8 dKH of alkalinity

I detail the rationAle for it here:

Reef Chemistry Question of the Day #200 Calcification and The Big Three Parameters

Reef Chemistry Question of the Day #200 Natural seawater has roughly the following parameters at 35 ppt: 420 mg/L calcium 7 dKH (2.5 meq/L) alkalinity 1280 mg/L magnesium. Let's imagine a typical coral reef aquarium with a mixture of different types of hard corals and coralline algae. Which...

www.reef2reef.com

 

[Randy Holmes-Farley]

I thought the ratio was 3 to 1 with magnesium and calcium in respective order?

You are confusing

1. the ratio of ions in seawater (1280 ppm Mg and 420 ppm calcium in 35 ppt normal seawater gives a ppm ratio of3:1)

with

2. The ratio of consumption of these ions, which is not related to the absolute levels present. Consumption ratios are about 10+ calcium : 1 magnesium. These values are easily verified by analysis of coral skeletons,

 

[Randy Holmes-Farley]

If so I'd honestly like to see some sources. Not questioning whether he's actively trying to spread misinformation, but when I basically read everywhere that it's a 3 v 1 ratio you sure do need some good evidence to support such claim... but in regards to your tank: How much is your calcium / magnesium? I am guessing your magnesium is roughly 3 times more than your calcium, not?

if you still want sources, they are here in Table 1 of my article:

Aquarium Chemistry: Magnesium In Reef Aquaria

This article details the nature of magnesium in seawater, how it is added, measured, and removed from marine aquaria, and how it impacts the maintenance of calcium and alkalinity.

reefs.com

 

[Zunador]

@Randy Holmes-Farley With him dosing so much magnesium, could it just be precipitating out of the water column or would it stay suspended?

 

[tbrown]

@Randy Holmes-Farley With him dosing so much magnesium, could it just be precipitating out of the water column or would it stay suspended?

That was my thought as well after these responses.

 

[Randy Holmes-Farley]

@Randy Holmes-Farley With him dosing so much magnesium, could it just be precipitating out of the water column or would it stay suspended?

Magnesium will not precipitate without taking out a huge amount of alkalinity. About 2.8 dKH for each 12 ppm of magnesium to make magnesium carbonate or magnesium hydroxide. Even more alk if it is coprecipitating with calcium.

 

[Icryhard]

You are confusing

1. the ratio of ions in seawater (1280 ppm Mg and 420 ppm calcium in 35 ppt normal seawater gives a ppm ratio of3:1)

with

2. The ratio of consumption of these ions, which is not related to the absolute levels present. Consumption ratios are about 10+ calcium : 1 magnesium. These values are easily verified by analysis of coral skeletons,

10+ calcium 1 magnesium? So calcium its consumption is higher than magnesium? If the answer is yes, how can my magnesium be consumed so much quicker?

 

[Icryhard]

if you still want sources, they are here in Table 1 of my article:

Aquarium Chemistry: Magnesium In Reef Aquaria

This article details the nature of magnesium in seawater, how it is added, measured, and removed from marine aquaria, and how it impacts the maintenance of calcium and alkalinity.

reefs.com

Thanks for the source Dr. Randy. Crazy to think you were writing stuff like this while I had just turned 4.

 

[Randy Holmes-Farley]

10+ calcium 1 magnesium? So calcium its consumption is higher than magnesium? If the answer is yes, how can my magnesium be consumed so much quicker?

Definitely. Calcium consumption is at least 10x magnesium, and sometimes much more than 10 if coralline is not the major calcifying organism.

As I stated, you cannot have higher mag consumption than calcium, and if it appears that way, it is test error, salinity changes, or water changes with a messed up salt mix.

Magnesium testing is unusually error prone and is very common. So common that I am nearly convinced it should not be measured as it causes mire trouble with false readings than it is worth.