Please check my math - adding Equilibrium, Limestone, and Magnesium Sulfate for GH - The Planted Tank Forum
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post #1 of 9 (permalink) Old 10-15-2009, 05:27 PM Thread Starter
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Please check my math - adding Equilibrium, Limestone, and Magnesium Sulfate for GH

I'm using RO/DI water. Based on Fertiliator, I need the following amount to get my 100 gallon tank within ideal parameter:

4 teaspoon of Equilibrium
4 teaspoon of Calcium Carbonate or Limestone
2 teaspoon of Magnesium Sulfate

This will give me about 10ppm of K, 9ppm of Calcium, and 4ppm of Magnesium. This will bring my GH to around 4 degrees and my KH to around 2 degrees.

Is this right? Can someone verify? I've read most people only add 1 teaspoon of Equilibrium to 50 gallon of water.
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post #2 of 9 (permalink) Old 10-15-2009, 07:18 PM
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Why use the CaCO3? CaSO4 or CaCl2 won't add to your KH, but CaCO3 will. Raising your KH is pointless unless you're trying to keep hard water plants. Don't worry about establishing a certain level of KH unless you're doing a rift lake biotope tank, if anything try to keep it low. Odds are the equilibrium and tap will take care of the Ca/Mg anyhow.

Equilibrium analysis:
Soluble Potassium (K20) 23.0% N (19.5% as K+)
Calcium (Ca) 8.06%
Magnesium (Mg) 2.41%
Soluble Iron (Fe) 0.11%

Right off the start, I see you're lacking both PO4 and NO3 I'll toss together some calculations for you on that.

We'll presume that you've got about 85 gal in actual water column, and that the rest is substrate and hardscape. That'd be about 320L for the sake of convenience.

So let's start with the equilibrium. I'll take the full analysis, and use this formula to give you nutrient levels:


where N is nutrient percentage.

K+: 12.991875ppm
Ca: 5.369975ppm
Mg: 1.425775ppm
Fe: 0.0732875ppm

Not too bad of a start. Perhaps a little short on the Mg. Unless you've got no calcium in your water, the Ca provided should be enough. K+ is 1/2 of what is required, but will be taken care of in a minute.

Now, as for N and P, again unless you're running a very low light tank, you're going to need to add some. Let's say 20ppm N and 1.5ppm PO4. KNO3 and KH2PO4 would be the easiest way to achieve these numbers.

KNO3 is 62.00501/101.10332 g/mol NO3. The following formula should provide 20ppm NO3 in 320L of column:

101.10332/62.00501*20*320 = 10435.628475828001640512597288509

So that's about 10.435628g KNO3

KNO3 also provides K+ at 39.09831/101.10332g/mol. So our existing quantity of KNO3 provides this much K+:

(39.09831/101.10332*10.435628/320)*1000 = 12.61133841ppm K+

Next up is phosphates as KH2PO4 which is 39.09831/136.0856722 g/mol PO4. You will need this much for 1.5ppm in 320L:

136.0856722/94.9714822*1.5*320 = 687.79723284133392202654282676869

Or about 0.687797g

Now to calculate the K+ levels, of which KH2PO4 is 39.09831/136.0856722 g/mol:

(39.09831/136.0856722*0.687797/320)*1000 = 0.61752690162773616368997881909276

Or about 0.617526ppm

Next up is calculating what sort of K+ levels you've got:

0.617526(KH2PO4) + 12.61133841(KNO3) + 12.991875(equilibrium) = 26.22073941

So in around 26ppm, which is very good.

In review, that leaves NPK and likely Ca and Mg satisfied with:

Equilibrium: 21.32g = 4 tsp
KNO3: 10.435628g = 2tsp
KH2PO4 0.687797g = roughly 1/8 tsp

If Ca and Mg turn out to be deficient in your water quality reports, I can give you calculations for that. If you can't get those numbers, I'd dose in another 5ppm or so of each, which I can show you how to do if necessary.

Now I'd suggest getting a micro/trace element to add. CSM+B, Flourish Comprehensive and Tropica Plant Nutrition are the 3 most popular choices. Any of them can work, I'm partial to CSM+B with the odd bit of comprehensive. They should take care of the rest of your iron demands when dosed properly. Let me know how you want to take care of your traces, and I'll do some more calculations.

For anything I've written above, if you aren't doing regular water changes to keep nutrient levels within bounds, you can just use the same proportions at a lower dosage to do more of a PPS style system.

If you want further help in the future, you can most easily contact me on, as well as a number of others with some good technical knowledge.

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post #3 of 9 (permalink) Old 10-15-2009, 07:34 PM Thread Starter
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Thanks! The reason I'm using Calcium Carbonate instead of Calcium sulfate is because I'm using 100% RO/DI water. This leaves me with zero KH. I'm using Calcium Carobnate to give me some buffering capacity. With zero KH, my ph would bottom out at around PH 5.7 - 5.8 with CO2 injection. I like to maintain my PH around 6.2-6.4 with Co2 injection, so that's why I use Calcium Carbonate.

I have just mostly swords and crypts and no stem plant so I don't mind if my GH and KH is a tad higher.

As for Micro, Nitrate and Phosphate - I'm still experimenting with two different senerios:

Senerio 1:
2-5ppm Nitrate
.2-.5ppm Phoshpate
.1 ppm iron supplied by Flourish

Senerio 2:
10-20ppm Nitrate
2-3ppm Phosphate
.1ppm iron supplied by Flourish and maybe adding more Florish Trace
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post #4 of 9 (permalink) Old 10-15-2009, 07:50 PM
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Why are you working from pure RO? Unless your tap is out of EPA bounds, you should be able to get by with at very least 25% tap. This would provide more coverage of micros/trace than just re-introducing everything.

If you want to do the 100% RO thing long term, I'd suggest learning your chemistry well enough to build your own traces. If you go this route, I'd applaud you for it; you'd have very high variable control. It is a lot of work though.

Crypts and Echinos definitely wouldn't have any problems with 5.8pH; many of them come from rain forest with hummic soils and nonexistent KH anyhow. Toss some apistos in and you'd have a lovely amazonian tope with some good spawns.

Don't bother with flourish trace; comprehensive has everything that trace does, plus other things, and more of it all. Flourish Trace is a waste of money, and I'd like to personally ask Greg Morin why he's pawning this snake oil along with reputable products.

Your first scenario looks pretty lean. I'm honestly not sure that plants can make use of nitrogen down at 5ppm; I've had deficiencies show at this level. It might be an idea to go with a high nutrient substrate like ADA AS or mineralized soil if you're going to try to keep a lean column. In this case, I'd get ready to dig up the tank and do new substrate in a year or two.

The second looks good. Try doing that for a while, and perhaps experimenting with increased iron levels.

Long term if paying for brand name is killing you, try DIY ferts. They're cheaper, and the results are just as good.

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post #5 of 9 (permalink) Old 10-15-2009, 09:16 PM
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Calcium carbonate is practically insoluble - even in RO water. It will dissolve VERY slowly - think about a snail shell in your tank - it is primarily calcium carbonate too.

Try baking soda to increase KH and one of the soluble calciums (sulfate or chloride) as suggested.

Tap mixed with RO should sound a lot better by now - and you might even start thinking about straight tap water.


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post #6 of 9 (permalink) Old 10-15-2009, 09:45 PM Thread Starter
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Rational for using senerio 1 (very lean water column nutrient) is because in the initial start up stage i'm planning to use 2WPG of power PC, with low plant density, and my tank is 30" tall. With low lighting, good Co2, heavy root fertilization, and low plant density - I think running lean is good for getting the plant established and ensuring that algae never get a foothold.

Once, everything is established and my plants are growing well, I may bump up my lighting to 3wpg and go heavier on fertilization like senerio two.

My other hobby is hydroponics. From hydroponics, I've read that PH plays a very important role in nutrient absorbtion. Ideal nutrient absorbtion takes place at 6.2-6.4 range. So that is why I want to increase KH to maintain my PH around 6.2-6.4 range. Isn't also having some buffering capacity good for the fish especially when doing water changes?

The calcium carbonate that I got are in very fine powder form. I've read that with CO2 injection, it should all dissolve within a few days.

BTW, my tank is 110 gallon - I've already accounted for substrate.
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post #7 of 9 (permalink) Old 10-15-2009, 09:53 PM Thread Starter
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I might be wrong but I've read baking soda are not the best product to use because it also adds unnecessary sodium. After all, it's sodium bicarbonate. Same deal with calcium sulfate becuase it adds extra sulfate - not that it's proven to be adverse but just stuff that your tank don't need. Whereas, Calcium carbonate creates no waste - it adds both calcium while increasing your KH. Granted it takes more time to dissolve.
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post #8 of 9 (permalink) Old 10-15-2009, 11:57 PM
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Wow! That's lot of calculation. I have my own spreadsheet to measure for my tanks but simply put, I use

Potasium Sulphate for K
Potassium Nitrate primarily for NO3 but it also adds K
Potassium Phosphate for PO4 but it also adds K (I my calculations, I first figure out how much KNO3 and K2PO4 to add for desired NO3 & PO4. The calculations tell me how much K is getting added, so I calculate how much K2SO4 to add to add up to my desired level)
Other than that I add chelated iron and CSM to micros. That's all.

Remember that you can (almost) never get exact measurements even if you are doing RO water. For argument, for the first time yes (may be). The next time you want to replenish nutrients, your water is no longer RO at that point so your original measurements do not hold true anymore (unless you are draining all your water and reintroducing full RO water again). That's why most people use EI which works pretty well. No calculations can tell you exactly how much to add each time since each tank is unique. I would use them for guidance only but do my own math and tests to figure out what works best for my tank. If you can afford, get a few of the test kits (nitrate, PH, GH, KH, phosphate, iron) and check them weekly for a few weeks till you get an idea of what kind of dosing regime works for you.

As far as using RO water, my opinion is that its a very costly approach that is really not necessary unless you have really hard water but want to grow really soft water plants like erios and toninas.

BTW, one of my tanks have KH=0, GH=3 and PH <6. I have toninas, rotalas, erios, hairgrass, crypts, cabombas and a whole lot more plants and a few fish (cory, GBR, pleco) surviving happily in it for months now.

Patience is the name of the game.

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post #9 of 9 (permalink) Old 10-16-2009, 03:20 AM
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I use my own spreadsheets as well, but calculating by hand is something everyone should know how to do. I think a good hobbyist should know why their targets are where they are as well, even if it's so simple as knowing that it's a common range for plants in their dry weight analysis.

I've used nearly pure RO, and I can honestly say that when you know where you're starting from, and what you're adding, how much you're changing, etc. you can control the absolute bounds. My problem was that I didn't have my own micros rolled. This is something I'm working on fixing. Still, doing it is for the sake of knowledge, not for a nice tank.

Now as for this sodium bicarb business, you're going to increase your sodium by 4.88ppm per 1dkh. I was doing some reading today, and a lot of toxicity sits not far off the 50ppm range. Personally I don't think it's doing the tank any favors to hit 20ppm even.

Personally I don't see the need to raise KH. I've kept near nonexistent KH tanks, Tom Barr has done the same without trouble, along with tons of different people with extremely soft water. Personally If I wanted to raise KH slightly, I'd do it with a little tap water. If I were going to the trouble of complete water quality control, I'd find a way to modify a calcium reactor.

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