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[AGA-Member] Magnesium nutrient issues
- To: "Aquatic Gardener's Association" <email@example.com>
- Subject: [AGA-Member] Magnesium nutrient issues
- From: Heather J Gladney <firstname.lastname@example.org>
- Date: Mon, 21 Feb 2005 19:42:50 -0800
- User-agent: Mozilla Thunderbird 0.7 (Windows/20040616)
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
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 babies.
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
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
I'm coming up with some odd numbers on Epsom salts from the ratios that
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 sodium.
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 again.
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
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
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 tank.
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?
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