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Calcium hydroxide in fresh water

M

MasterMoriarty

Seedling
Joined
16 Jun 2009
Messages
12
Hi all

I know absolutely nothing about the chemistry concerning the chemicals dosed in planted aquaria, mainly I go on what people like yourselves and The Barr Report site say.
I've read that using bi-carbonate of soda adds sodium to the water when used to raise KH/pH, so I wondered if calcium hydroxide (Kalk powder) could be used instead.
I know it takes a very small amount of it to raise the alkalinity & pH of R/O water to acceptable levels but I was wondering if anyone knows how much a given amount of it would raise the calcium level by.
Another reason I was thinking about calcium hydroxide is, when using CaSo4 & MgSO4 as GH booster the CaSO4 is hard to dissolve and it takes a lot of it to do the job.
From what I remember from Fluidsensor CaSO4 contains 23.3% calcium, does anyone know what percentage calcium hydroxide contains?
I was thinking if calcium hydroxide could be used instead of the bi-carb, then if I knew how much calcium it adds I could reduced the amount of CaSO4 needed in the GH booster.

I use straight R/O - D/I water for water changes because I use it for my reef tank anyway so it's no great hassle to have some spare sitting around. Besides my tap water can be pretty dodgy sometimes.

Hope this makes sense 😳

Cheers
 
Hi,
Calcium is about 55% by weight in Ca(OH)2, a medium strength base that will definitely raise pH but will not have a significant effect on carbonate hardness - because KH is a measure of the carbonate/bicarbonate content of the water. Since pH is irrelevant the only advantage of this powder is the calcium addition which you don't really need in abundance. Best to stick with sodium bicarbonate for adjusting KH, which you don't need a whole lot of. Anywhere between 2 and 4 will do. Likewise with GH. If you use only lime powder then all you are adding is calcium. You will still need to add magnesium so I see no advantage over GH Booster. In a freshwater planted tank calcium just needs to be non-zero. This is not a big deal like in reef setups. If you're having difficulty dissolving GH Bosster then you are using way too much and your GH targets are way too high.

Cheers,
 
Hi

Thanks for the reply.
I just wondered if using Kalk would reduce the amount of CaSO4 needed and raise the KH so I could kill two birds with one stone, 🙄 but if it only adds calcium I'll stick with what I've been doing.
The tank is 115 litres and I change about 80 litres/week. It's pretty heavily stocked with fish and about 50%+ planted.
On Sundays I've been adding 1/16 tsp of bi-carb per 5 litre R/O at water change, which I think gives a value of approx. 3.3 dKH & a pH of 7.4
I also add 5g of CaSo4 + 3g of MgSO4 at water change and the same again (Ca + Mg) on tuesdays, to give approx. totals of 20ppm Ca & 5ppm Mg. I dose the GH booster over two days because the CaSO4 takes so long to dissolve but I suppose I could mix it well with some tank water or R/O and then pour it in.
Do these amounts sound OK for this tank volume? And is it OK to split the GH booster or should it be dosed all at once?

Thanks again
 
Well, as I suspected I really think you're way over the top for GH. I just don't get why you need that much Calcium. You ought to do OK by dosing the standard GH Booster values of 1/8 teaspoon per 100L as shown on this page=> AE's GH Booster which for your tank would be a little over 1/8 teaspoon or about a gram. You're adding something like 16X more than you need. No wonder it doesn't dissolve. :shock: Are you trying to make your own Kalkwasser :?: :?:

In any case a KH of 3.3 sounds pretty good to me, so there's little danger of toxic sodium levels. I reckon if you cut down on the GH life will be simpler. If you start to see any deficiencies you can double that 1/8 teaspoon value and you'd be OK.

Cheers,
 
OK
Either there's a lot of inconsistency in this hobby or I've made a huge miscalculation in my ferts :!:
You say I'm using 16x more than I need, if that's the case then can you explain why 20ppm calcium & 5ppm magnesium is 16 times more than is needed? Because this is what is being suggested here http://www.theplantedtank.co.uk/RO.htm
I'd love to know what's in the GH booster here, http://www.aquaessentials.co.uk/index.p ... ts_id=1376 if it only requires 1/8 tsp/100L, as opposed to what is being recommended here http://www.fluidsensoronline.com/epages ... in_planted
Going by my calcs. adding 0.043g per litre of CaSO4 to 115L = 4.945g which gives of 10ppm calcium and adding 0.05g per litre of MgSO4 to 115L = 5.75g which gives 5ppm of magnesium. Or am I missing something here?

Cheers
 
You could use calcium hydroxide to add Ca++ and raise the alkalinity but I wouldn't recommenend it as it's a pretty caustic compound. Although it doesn't add any carbonate it does raise alkalinity which is what your KH test kit measures. Remember most plants don't need carbonates and actually do better when the cabonate value is low.

I'd try and keep it simple and use calcium sulphate and epsom salts with a small amount of sodium bicarb if you can't find potassium bicarb. Just dose at water change time rather than splitting through the week. Calculate the amounts based on your water change volume rather than tank volume or you'll find the concentrations drifting up over time. Plants require a small amount of chloride which is why I add it. Think you can get a low sodium salt in the supermarket.

Your calculations are correct and seem fine to me. You can use my dosing calculator to work all these out - http://www.theplantedtank.co.uk/calculator.htm

2 teaspoons (~10g) of Seachem's Equilibrium dissolved in 50 gallons (US) of water adds the follow amounts:
Calcium - 4.9ppm
Magnesium - 1.4ppm
Potassium - 10.8ppm

Also added are small amounts of ferric sulphate and manganese sulphate.

GH Booster is pretty similar to Equilibrium.

I have tried Equilibrium in the past and never found it to be that good. It's good if you wish to add a bit extra GH to your water but no good for using it to reconstitute RO water IMHO. It sends potassium and TDS values through the roof, especially if you dose something like Estimative Index.

HTH
James
 
Thanks for that James

I'll dose Ca/Mg according to the water change volume then.
I did a search for potassium bicarb but couldn't find it anywhere, is it sold under a different name? Were do you get yours from? I'm in N. Ireland.
I dose EI, all dry ferts, + EasyCarbo, non CO2.
Got some akadama at the weekend (ADA AS too expensive 🙄 ) so looking forward to re-doing the tank ASAP.

Cheers
 
I finally bought a GH test kit (Tetra liquid type) and my tank is at 8 dGH.

I've reduced the Bi-carb to 1/16 per 10 litre aiming for a KH of about 1.9

Does anyone know if the tetra kit is accurate?
Also what ppms of Ca & Mg does a GH of 8 represent?

Cheers
 
No hobby grade test kit is accurate. Also it cannot determine what percentage is Ca and what is Mg. You would have to get dedicated Mg and Ca test kits which really are not worth it generally.

Cheers,
 
Thanks

Looked at the separate kits yesterday, definitely wouldn't consider spending £13 odds on either of them. The GH one was dear enough at £6.50 especially if as you say it's inaccurate.
Guess I'll just go with keeping things simple and let the plants do the talking and hope I can keep things in order 🙄

Cheers
 
Most test kits aren't as bad as people like to make out. The errors come from how the tests are done and reading the scales. Things like when it says hold the bottle upside down it means upside down and not at a 45 degree angle. The GH and KH ones I've always found to be pretty accurate. PO4 and NO3 can cause some people problems as there is an extra step in the procedure, but generally I get fairly consistent results, even when compared against standards. Out of the cheap bunch I find Hagen are the easiest to use. Then again these days I very rarely use them, only when I'm doing a trial in something.

Determining Mg and Ca from GH isn't too hard but you have to purchase a Ca test kit first. Most Ca test kits are aimed at reef tanks so as freshwater has much less Ca the test is very sensitive. I always double up the test volume to get a bit more accuracy. Once you know the Ca content you can work out the Mg.

James
 
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