High GH, but not enough Mg - The Planted Tank Forum
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post #1 of 13 (permalink) Old 10-24-2015, 05:29 PM Thread Starter
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High GH, but not enough Mg

Mg deficiency has shown up suddenly, I guess because the GH of my tap water has decreased slightly, but still fairly high at around 7 degrees. The water report says around 7 ppm of Mg, but apparently it's not quite adequate. 50% weekly changes should only be adding about 3.5 ppm.

This week I added Epsom salt, about 3-4 ppm worth, but how will this affect the GH? I don't want to increase hardness too much and I really don't want to purchase an RO unit unless it's absolutely necessary to get enough mg in the water. I have soft water fish- harlequin rasboras, neons, CPDs. My fish don't breed, except for I'm guessing the CPDs (I saw a single tiny fry once), but seem to be fine in my water and are otherwise very healthy and colorful.
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post #2 of 13 (permalink) Old 10-24-2015, 05:55 PM
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I doubt that you have enough magnesium in your tap water. When you add more it will raise the GH, but I don't think it will raise it too much. I think I would try to add about 20 ppm of magnesium. (I would do more research first, though. One place to look would be https://www.plantedtank.net/forums/11...-regimes_.html )

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post #3 of 13 (permalink) Old 10-24-2015, 11:39 PM
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Mg++ (ppm) * 4.12 / 17.8 = dGH

7dGH - 7ppm Mg++ = 40ppm Ca++ give or take.

An RO unit will not help to get MG in the water, Epson salt will do that.

Since GH boosters on the market today add Ca at a ratio of around 8:1 with Mg, your Ca:Mg ratio is around 5.7:1, and plenty of people grow plants fine at dGH <7, I suspect it's not the level of Mg in the water that is the issue, but rather the balance of ions in the water. Check the water report for potassium and sodium levels.

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post #4 of 13 (permalink) Old 10-26-2015, 03:06 AM Thread Starter
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Quote:
Originally Posted by Hoppy View Post
I doubt that you have enough magnesium in your tap water. When you add more it will raise the GH, but I don't think it will raise it too much. I think I would try to add about 20 ppm of magnesium. (I would do more research first, though. One place to look would be https://www.plantedtank.net/forums/11...-regimes_.html )
Thanks. I must have looked in the wrong place the first time, there are two parameters given: Mg, and magnesium hardness. There are no units given for either, just numbers, so it's confusing. Hardness is given as both mg/L and gr/gal, which is nearly the same as dGH. 122 mg/L total, mg hardness is 30, Ca hardness is 92.

Do you mean 20 ppm total weekly? Since a 50% water change actually adds about 15 ppm mg, I could try adding another 5 ppm weekly.

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Originally Posted by Audionut View Post
Mg++ (ppm) * 4.12 / 17.8 = dGH

7dGH - 7ppm Mg++ = 40ppm Ca++ give or take.

An RO unit will not help to get MG in the water, Epson salt will do that.

Since GH boosters on the market today add Ca at a ratio of around 8:1 with Mg, your Ca:Mg ratio is around 5.7:1, and plenty of people grow plants fine at dGH <7, I suspect it's not the level of Mg in the water that is the issue, but rather the balance of ions in the water. Check the water report for potassium and sodium levels.
Right, the RO water would be mixed in so I could add more Epsom salt without increasing GH.

After a closer look at the water works website (see above), I'm not sure it's a Mg issue either. I looked, but nothing is given for K or Na whatsoever. I'm adding about 8 ppm potassium in total, 3x weekly, so 24 ppm weekly. Could that be a problem if there is already potassium in the tap water? Staurogyne repens leaves have light patches between the veins.

Last edited by Darkblade48; 10-28-2015 at 04:56 AM. Reason: Please use the edit function for back to back posts
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post #5 of 13 (permalink) Old 10-26-2015, 03:51 AM
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What are the numbers for just Mg and Ca (not hardness)? edit: Nevermind, 7ppm Mg++ = 30ppm Mg as CaCO3 (hardness).

Can you link the report?

As best I can tell, you can't overdose K unless you're being completely stupid.

Personally, I would bump the K doses to 12ppm or so and observe that for a week or two. It'll probably want some more Mg, but I'd do K first for observation.
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post #6 of 13 (permalink) Old 10-26-2015, 12:45 PM Thread Starter
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Thanks, yeah mg is 7.35, Ca is 36.7. Here's the link:
http://www.dmww.com/water-quality/water-quality-data/

Basic data is given on that page, but you have to run a query to get other parameters. Here's the link (select Fleur treatment plant): http://www.dmww.com/water-quality/wa...-quality-data/
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post #7 of 13 (permalink) Old 10-26-2015, 12:52 PM
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That Ca:Mg ratio is just fine. I would look elsewhere for the deficiency. How is the iron level?
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post #8 of 13 (permalink) Old 10-26-2015, 02:44 PM Thread Starter
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I had considered iron or other micronutrients, which is why I recently doubled micro dosage just to cover all the bases. Previously, I was adding 1/32 tsp of plantex csm+b along with 2 mL flourish iron. This is a 20 gallon long, so that would be roughly 0.37 ppm Fe altogether, 3X per week. I recently increased plantex to 1/16 tsp 3X weekly, flourish iron still the same at 2 mL, so now total Fe added is roughly 0.48 ppm, 3x per week. It's probably still too soon to tell if it will help.

Here's a photo of the s. repens, sorry about the poor quality.
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post #9 of 13 (permalink) Old 10-26-2015, 03:12 PM
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Looks like Mg, but could be zinc or iron. But the lower leaves are patchy too, so I don't think iron. Hope someone more experienced can help.
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post #10 of 13 (permalink) Old 10-26-2015, 07:47 PM
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Quote:
Originally Posted by Diana View Post
That Ca:Mg ratio is just fine. I would look elsewhere for the deficiency. How is the iron level?
I agree about the Mg. Sorry, I missed something with my first reply.

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post #11 of 13 (permalink) Old 10-27-2015, 02:13 PM
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If it started on the older leaves, it's probably N, and if it started on the newer leaves, it's probably Fe.

P deficiency can look similar, but it's relegated to old growth in my experience, and an increase in GSA helps confirm.

Feel free to edit.
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post #12 of 13 (permalink) Old 10-27-2015, 03:37 PM Thread Starter
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I did have an obvious P deficiency a month ago after changing the LED fixture to a Finnex 24/7. I increased KH2PO4 dosage, and saw an improvement at first. Now that I think about it, it's possible that once P became sufficient, a N deficiency followed. The newer leaves do not look pale, but some of the new growth is curled and small. I recently ended up increasing the dosage of everything else as well. The thing is, I still haven't noticed much improvement a week later, so I checked the water report, and after misreading it I thought it was Mg deficiency for sure. :/

Since it's the star repens that is the most affected, the problem could also be the flow near the bottom, however it's such a shallow tank this shouldn't be an issue. It's never been an issue before, but I guess it could be a combination of the presence of more plant mass reducing the overall circulation, and increased demand due to the new light fixture. I think for now I'll just continue the new dosing schedule and wait to see if things improve.

Thanks!
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post #13 of 13 (permalink) Old 02-19-2016, 02:35 AM
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Looks like zinc deficiency. Zinc is a variably mobile micro-nutrient and can have symptoms of interveinal chlorosis in both old and new growth. With a zinc deficiency plants are highly sensitive to both high light and heat. A deficiency can also cause membranes to become leaky, this can lead to GSA and other types of algae.

Last edited by Silversea; 02-19-2016 at 02:40 AM. Reason: Added information
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