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Re: [AGA-Member] Magnesium nutrient issues

Larry Lampert wrote:


A couple of comments and a couple of questions....
You stated:

advise. dGH - dKH = additional alkaline metals

such as Na, Mg, and so

on. One point of the difference is the soda I've

been adding. Local

waters are alkaline but not dolomitic, so I'd

suspect the remaining

point, from the source tapwater, is also mostly


Magnesium and Calcium are components of GH. The alakaline earth metals are the would be like barium, or other rare elements. These are not commonly seen in measurable quantities in tap water in the US.

As far as I remember Sodium does not add to alkalinity

I should have rechecked my Krib printouts (thought I had--must have glazed over on these) Rechecking some of the Krib's archived water hardness posts, 16 Dec 1997 Larry Frank was saying that GH measures only Ca and Mg, KH measures only bicarbonate and carbonate anions, not sulfates or other anions. He also comments that in most freshwaters most of the cations are Ca:Mg in 3:1 ratio, but levels of GH and KH will often be similar.

It does of course add to TDS. If you are
concerned with Na levels contact your local water
utility and ask for a copy of their annual water

Our is online, so I was able to yank some numbers. (see below).

I am also not sure about your magnesium ratios you are
trying to chieve. CA and MG are macro elements. The
plants use them for osmotic balance as well as
consuming themin trace amounts. The ratios between CA
and MG are usually 4:1 or 3:1. I think what you read
on Chuck's page was the minimum amount of 5-10 ppm MG.

Sigh of relief!

Increasing the MG will increase your GH but it will
affect your buffering capacity. If you add a carbonate
or bicarbonate like baking sode that will increase
your alka;inity or the ability of your ater to resist
a downward change in pH.

When I rechecked my copies of Krib posts re: hardness and CO2, I found one water hardness post put up by Larry Frank back in 1997 in the CO2 archive of the Krib. He said adding carbonates would push the equilibrium back toward a more alkaline situation. You're quite right, it's the carbonates doing so, not the Na.

If you are concerned with your CA:MG ratios you can
use Seachem's equilibrium instead of the dolomitic
lime and epsom salts. Equilibrium will give you a
correct ratio out of the jar.

Great idea, thankyou--I'm really tempted to toss aside the calculations!

I would contine to use
Baking Soda for raising Alkialinity unless you do
indeed have an elevated level of soium in your water
like Cheryl does. I would not assume this to be the
case until I read a water report.

I found local water report for 2003 and had kept it for 2002. Not an easily read report for lay people, IMHO.
It uses separate 85% surface water figures and 15% ground water figures, so you have to run the totals yourself.
With those percentages of the surface/ground mix (which could vary across the area by source), on average:

2003 Na: surface 5.4 ppm ave., ground water 25 ppm ave. = 8.3 ppm total ave.
2002 Na: surface 4.8 ppm ave., ground water 30 ppm ave. = 8.6 ppm total ave.

2003 Ca: surface 13 ppm ave., ground water 23 ppm ave. = 14.5  ppm total
2002 Ca: surface 14 ppm ave., ground water 33 ppm ave. =  16.9 ppm total

2003 Mg: surface 3.8 ppm ave., ground water 14 ppm ave. = 5.3 ppm total
2002 Mg: surface 3.6 ppm ave., ground water 20 ppm ave. = 6.1 ppm total

(which gives an interesting ratio, Ca:Mg surface=3.4, 3.9 Ca:Mg ground = 1.6, 1.7, and tap average Ca:Mg = 2.7, 2.8,
in other words, a ratio of Ca: Mg = 10:3 to 10:4 in my tapwater. Quite a ways off from 3:1, or 4:1! Sounds like the Mg in the makeup water does need to go way up!)

2003 Hardness: surface ranges from 27-74, ave. 44 ppm, ground water ranges 70-156, ave. 112 ppm.
Or 54.2 ppm total ave.or (dividing by conversion ppm/dGH=17.9) 3 dGH, which is about what I measure out of my tap.

2002 Hardness: surface ranges from 27-58, ave. 42 ppm, ground water ranges 112-278, ave. 164 ppm..
Or 60.3 ppm total ave. or (dividing by conversion ppm/dGH=17.9) 3.4 dGH.

2003 nitrate, "None detected" surface waters, 5.2 ppm ground water = .8 ppm total ave.
2002 nitrate, .38 ppm surface waters, 7.3 ppm ground water = 1.4 ppm. total ave.

When I did nitrate test on tap, I got zip-1 ppm, below threshold on the Tetra test kit.
So I probably ought to count that about 1 ppm of my tank's nitrate is right from the tap, particularly in summer!
ie., don't use the wells around here, and count on higher nitrate numbers in a drought year!

I think you should just raise the GH to 4-6 by using
equilibrium and just forget about it. It is one thing
less to worrry about while you are trying to dial in
your traces.

Currently your CO2 according to the chart @pH 7.4, dKH
4, dGH 6 is only 4.7. This is still your main problem

I've been dialing the CO2 and bringing down the pH very gradually, while adding more lime and soda at water change.  At last testing, I had kH 4, GH6, with pH at 7.4.  I want to bring that down to 6.8-6.4.


You need to push your CO2 up to 20-25 and then you
will likely have to readjust your traces as consuption
goes up.

I also use Fe (.2ppm) as the proxy as recommended by
Tom Barr, Roger Miller and others to set my trace
levels. You are going to get your traces in line AFTER
you get the CO2 issue resolved. Once this is done then
you can start fine tuning your dosing and water in
relation to the amount of light and depth of your

You also have a lot of light at nearly 4 watts/gallon.
You may want to dial it back to a little less than 3
watts/gal until you get your tank balanced.

I have shortened the photoperiod a bit, down to just under 10 hours. I'm already using a midday break to let all the bulbs cool when it's hot. Not a problemn now, but it will be in summer.
If I wanted to tone down the wattage as well as the heat, I could run each bulb on its own timer in sequence, so at any given time there's one out of 4 bulbs turned off for a cooling break. This might cost longevity for such frequent on/off all the time, but it might also extend the bulb life because they're not cooking the cover glass hot enough to fry eggs on!

that the more light and CO2 you have the more traces
you will need to be available to the plants so the
less margin you have for error in your dosing.

Thanks very much for your help!

Regards Larry Lampert Dallas, TX

--- Cheryl Rogers <cheryl@wilstream.com> wrote:

No one ever answered this. What a drag. I was
looking forward to it.


Heather J Gladney wrote:

My 90 gallon tank (actual gallons about 76) has

lots of long stringy

algae,BBA, and one large old SAE.
As it's a tall hexlike diamond shape, I've got

power compacts on it, 2 X

55 watt and 2 X 96 watts, for total 302 watts, or

not quite 4

watts/actual gallons.
It generally has 0 nitrite and about 12 ppm

nitrate, probably due to

fish + food.
I'm not certain how many inches of fish it has

because the Corydorus

catfish breed in there, and I keep finding new


It used to have CO2 injection issues, and CO2 was

off completely for

about 2 weeks.
I'm trying for a community tank balance, as I'm

keeping both Cardinal

tetras (soft acid water) and Cryptocorynes that

like hard alkaline water

(bad owner!!). In fact, the C. balansae grew

better when my CO2 line

was down.
I think I finally got the CO2 supply fixed this

weekend, thanks to

helpful advice from folks here.

Now I'm thinking about the nutrient dosing to work

on that hair algae

and BBA.
I'm coming up with some odd numbers on Epsom salts

from the ratios that

people suggest.

Normally, with CO2 injection, the tank was at pH

6.8-7.0, dKH 5-6, dGH 7-8.

Without the CO2, the tank went up to pH 7.4 - 7.8,

same dKH and GH.

Tap has KH 2, GH 3, so some months ago I started

adding powdered

dolomitic limestone (from Greg Watson) and baking

soda to bring makeup

water one point each to dKH 3, dGH 4. This isn't

as high as some

advise. dGH - dKH = additional alkaline metals

such as Na, Mg, and so

on. One point of the difference is the soda I've

been adding. Local

waters are alkaline but not dolomitic, so I'd

suspect the remaining

point, from the source tapwater, is also mostly


Which says there's hardly any Mg in there.

Awhile back someone reminded me of Tom Barr's

advice, and suggested

bringing up dKH to 4-5 and add some soda for

better pH buffering.

Because of that, and to better match the tank's pH

without any CO2

injection, on my latest 30% water change, I

doubled the limestone and

soda amounts as I got the CO2 injection going


Now, with CO3 injection started, the tank tests at

pH 7.4, dKH 4, dGH 6.

The difference is 2 points, just what you'd expect

from doubling my

previous soda amount in the makeup water.
I also added fertilizers that include macros, Mg,

Fe, traces, and so on,

but clearly not enough Mg to affect the dGH-dKH

hardness difference very

As I adjust the CO2 injection, I'll bring that pH

down gradually to

6.8-6.9 to get better CO2 percentage.
But perhaps I ought to increase my limestone and

Mg amounts too.

That made me start to recalculate my dosing drops.

Please correct me if I'm wrong, but could I

increase dGH by skipping the

soda and adding Epsom salts for Mg instead? This

should increase

general hardness for buffering the pH, and the

plants would like Mg

better anyway.
I thought of this because I saw comments noting

that the ratio of lime

to Epsom salts should be roughly 4:1, or:
CA(CO3) : MgSO4, should be 4:1, which ties my dKH

to how much Epsom

salts I add.

Working from "the ideal Mg amount":
My hardness test kit instructions show 17.9 ppm =

1 degree for both dKH

and dGH.
Chuck Gadd's nutrient calculator page suggests the

guideline of 5-10 ppm

of Mg, but other comments suggest it can be more.
If I maintain the ideal Mg of 5-10ppm, that 4:1

ratio gives 20 - 50 ppm

CA, or dKH =1.1 - 2.8, which I thought was pretty

soft water. A lot

softer than what I've got going!
But list comments note that many plants like hard

water, that it can go


Working from the hardness I've already got:
With current dKH of 5 - 6, or 89.5 -107.4 ppm Ca,

a 4:1 ratio that gives

22.38 - 26.85 ppm Mg.
That is double the high recommendation. Also, it

requires adding 4 -

4.5 tablespoons of Epsom salts dry directly to the


This sounds like an awful lot!
It also adds that same amount of sulfur, and I

planned to add sulfur

elsewhere by using potassium sulfate (K2SO4) as a

K source.

(I don't want to use KNO3, because the N is plenty

high in this tank

right now--I hope that it'll go down if I can get

the plants growing

Do we have any guidelines on how much sulfur is

too much?

Also, how much change in dGH does that much Mg do?

Don't think I'd need

to add any baking soda, though!

Whic leads down to the final question, would it be

okay to push up the

Mg to keep the ratio with Ca intact, or should I

leave it at Chuck's

5-10 ppm and a lower calcium amount and lower dKH,

which I suspect the

fish would like a little better?

Cheryl Rogers, Membership
Aquatic Gardeners Association
AGA-Member mailing list

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