[Wet Thumb Forum]-Calcium dosing to increase GH

[Dave P]

While sulfur and hydrogen can combine to produce a dangerous and unpleasant gas, I don't know if the small amounts added by Equilibrium are at all significant to that process. I am an agnostic as far as that is concerned.

By my estimates, there is approx. 0.57 g of sulfate -- over half a gram -- in every gram of Equilibrium. If one follows the label, raising GH by 3 degrees would require the addition of 16 grams (1 tablespoon) of Equilibrium for every 20 gallons of water. Using the above figure, this would mean that 9 of those 16 grams is sulfate. In my opinion, this is not a small amount.

I do agree, however, that more research on this issue would be desirable, and that it would be interesting to see what Seachem would have to say.

Dave

[dwalstad]

Originally posted by Dave P:

By my estimates, there is approx. 0.57 g of sulfate -- over half a gram -- in every gram of Equilibrium. If one follows the label, raising GH by 3 degrees would require the addition of 16 grams (1 tablespoon) of Equilibrium for every 20 gallons of water. Using the above figure, this would mean that 9 of those 16 grams is sulfate. In my opinion, this is not a small amount.

Dave

Hardwater in nature contains bicarbonates, sulfates, and chlorides. Wetzel (Limnology, p. 183 of his 1983 edition) shows the sulfate concentration between 17 and 35 mg/l (the chloride range is 8 to 17 mg/l) of five naturally hardwater lakes. Just for fun, I'm going to follow up on Dave's post, to see how his Equilibrium addition compares to the sulfate concentration in these natural hardwaters.

20 gal X 3.8 liters/gal = 76 liters

If naturally hardwater contains 35 mg of sulfates/liter, the tank contains a total of 2,700 mg (35 mg sulfates/liter X 76 liters). And 2,700 mg = 2.7 g. This is less than the 9 grams of sulfates added by Equilibrium dosing to get a GH increase of 3 (according to Dave's calculations).

Adding a CaCl2/MgSO4 combination better mimics the natural condition of having a mixture of anions, not just one. It also lessens potential H2S problems. Potting soil substrates, at least mine, have been quite anaerobic (fresh ones bubble like mad for months). I am fairly sure that they have a Redox low enough for H2S production.

That said, I have never heard a single complaint about Equilibrium, and many hobbyists defend it vigorously.

[Dave P]

Thank you Diana for posting this data on sulfate and chloride concentrations found in hardwater lakes. I just might use some of my upcoming vacation time to visit the university library nearest me and find this study that Wetzel published in Limnology.

If anyone is interested in how I determined how much sulfate is present per gram of Equilibrium, please leave me a PM with an email address and I will gladly send you a Word doc showing the stoichiometry and results. If I had more time, I'd make the document look prettier than it is; however, it is quite legible in it's present state.

Dave

[aquabillpers]

This thread is extremely interesting to me, in part because it is bringing back long forgetting memories of moles, molecular weights, and similar, personally-unused concepts and, in part, because it does present evidence that supports the possibility that Equilibrium can cause problems. But I remain an agnostic on that.

One question that I have is, what happens to the SO4 when it splits from the CA? I suspect that it undergoes further changes, rather than just sinking into the substrate. Some of it is undoubtedly absorbed into plant tissue; perhaps some combines with other chemicals and becomes insoluble. I don't know.

While walking through swamps I've often encountered large amounts of H2S. (It can be easily identified without expensive lab equipment. I wonder if high sulphates in the water by themselves are responsible for this or if there is some other process involved that grabs whatever sulphur is available to combine with the hydrogen. I don't know that, either.

It would be interesting to conduct an experiment with two natural tanks with anaerobic substrates and water with low sulfates. CaSO4 would be added to one and the amount of H2S measured. The point at which H2S becomes a threat would also have to be predetermined.

Bill

[aquabillpers]

Here's Seachem's reply to my question. It seems to support both views, which is good, since both
are "right".

"Dear *****,


As Diana Walstad said, in the vast majority of tanks Equilibrium is fine to use. Theoretically a tank with a large amount of anaerobic areas could have problems with hydrogen sulfide production. In her book she also mentions that oxygen released by the roots and soluble iron give the plants some protection. We have not experienced this problem nor have we had any reports from customers on this problem.


Best Regards,
Seachem Tech Support~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Seachem Laboratories, Inc. http://www.seachem.com 888-SEACHEM
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[dwalstad]

Originally posted by Billpers:

Q #1: One question that I have is, what happens to the SO4 when it splits from the CA?

***Plants will take up some sulfate for their sulfur needs (they need almost as much sulfur as magnesium). See "Critical Concentrations" on page 105 in my book.

The remaining sulfate diffuses throughout the water. I don't know of any sulfate salt that is insoluble. That's why Equilibrium probably dissolves very quickly. Dissolved salts (including sulfates) will diffuse into the substrate so that the concentration in substrate water will probably approximate what's in the water.
**************

While walking through swamps I've often encountered large amounts of H2S. (It can be easily identified without expensive lab equipment. I wonder if high sulphates in the water by themselves are responsible for this or if there is some other process involved that grabs whatever sulphur is available to combine with the hydrogen. I don't know that, either.

***Bacteria use sulfates as their electron acceptor and convert the sulfates to sulfides (reaction on p. 67 my book). The sulfides readily combine with metals in soil like iron, zinc, manganese, etc to form precipitates. If there's no metals to precipitate out the sulfide, then you have H2S. That's why I got major toxicity when I added sulfate-contaning fertilizers to potting soil (made up mostly of organic matter and with very little metals), but got absolutely no toxicity when I added same fertilizer to my garden soil.

Brackish water swamps along the coast will have more H2S than freshwater swamps that are further inland. That's because ocean water contains lots of sulfates.
**********

It would be interesting to conduct an experiment with two natural tanks with anaerobic substrates and water with low sulfates. CaSO4 would be added to one and the amount of H2S measured. The point at which H2S becomes a threat would also have to be predetermined.

Bill

Experiments are always fun. I would compare CaSO4 with CaCl2 (OR MgSO4 with MgCl2). The only variable then is the sulfate.

I was pleased with Seachem's response to your query. Thank you for posting it.

[javalee]

I just wanted to update everyone interested in Ca++ Mg++ supplementing. I raised the GH of my 10g from 3dGH to 9dGH with CaCl2 and MgSO4 (epsom salt) thinking I would rarely have to add it again. However, I've noted that the plants must be sucking the Ca++ and Mg++ out of the water at a pretty good rate. Within 2 weeks of the first addition the GH was back down to 6 or 7. This week I checked and it was down to 4dGH!

So I'm adding it about every two weeks now. Of course, I just top of evaporation loss with tap water, and when doing water changes (which I'm doing more of than most natural tank people do lately as the DOC leach out of the soil) I replace with 8dGH water.

It's not a bad regimen as I've memorized about how much to add to get the 4:1 ratio of Ca++ and Mg++. I can usually test it and get the right amount within two tries. The fact that it's disappearing makes me think my plants are better off for getting an ample supply! The hornwort is finally growing as hornwort should---requiring thinning 2xs per week!

Below is a picture after serious thinning and pruning of hornwort, floating plants, and hygro.

[dwalstad]

Javalee,

What a gorgeous tank! You must be very pleased.

I think that some of the water calcium precipitates out (as calcium phosphate, calcium carbonate, etc). Scientists that analyzed filter biofilm contents found calcium phosphate and other precipitated salts in the filter gunk. Also, some precipitated calcium may end up in the substrate. None of this will hurt anything and probably will help.

In any case, the dosing you're doing is clearly working.

[javalee]

Thanks so much Diana! I am very pleased with your method! It never even occurred to me that the ca++ and Mg++ could be precipitating. Thank you for explaining that. I wonder if I should still be adding it? I guess if it's not measurable it's not available to plants? I don't know, but yes, the plants are doing well!

[DataGuru]

Here's a good thread on Koivet where Roddy Conrad explained the chemistry behind how calcium and magnesium help stabilize pH and what happens when it precipitates out. In the example they were talking about a pond with an algae bloom and low GH had pH spiking very high even tho KH levels were fine.