DIY Buffer PH & DKH Increase

[Jimbo]

Just emailed Tom(tdwyatt) regarding the correct proportions to mix baking soda with washing soda to make a correct buffer. I've mixed up 1 x 1/2ts washing soda and 6 x 1/2ts baking soda in one liter of water, added this over a two day period and it increased my PH by about .1 and alk 4dkh in 40gal's water. This stuff is really strong so ADD SLOWLY, drip it.

I used the arm & hammer pure washing soda. I've heard that in canada they have a perfumed washing soda, this will not due. There's a pic of the ingredients you will need.

Here's what Tom said.

Mix 6 parts NaHCO3 to 1 part Na2CO3, but test this to see how high it drives your pH after addition. If it is no more than 8.9 or so, then use this mix. Weight is close enough that you can use volumes to attain this, but by weight would be more accurate if you have a balance.

If the pH after addition to seawater goes to 9.5 or 10 and stays there for more than 5 minutes, then go to 8:1 bicarb to carbonate, which will not raise the pH so drastically. You should dissolve the final product in a goodly volume of top off water and drip it in over 5 minutes or so to prevent big temporary swings in seawater pH, which will also have a tendency to gas off some of the alk as CO2 gas (which accounts for the reason that bicarb by itself will raise pH initially, then drop below 8.2, then come back to 8.2 or so after equilibration.) drip into rapidly moving water (like into the overflow or into the drains from the overflow in the sump.)

HTH!

~T

[yardboy]

Considering that baking soda is food grade and washing soda is not, wouldn't it be safer to heat the baking soda in an oven to convert to sodium carbonate?

[Jimbo]

Yard Boy I didn't know you could cook it and turn it into sodium carbonate.

But have heard many others that have written that they use arm & hammer washing soda without any ill-affects to there tanks. Wet Web media on the archived question and answers is where I saw washing soda mentioned, although that does not mean it's very pure.

[PaintGuru]

I've added a mixture of both with no problems. I usually dump a jar full of water with 1 tsp of mixture into my sump (I'm not patient enough to drip). It's worked well so far.

[yardboy]

I've got a stock solution of sodium carbonate (whichever way you choose to get it!) and of calcium chloride that I got from Advanced Aquarist and I just use 50ml doses at a time, dumped straight into the sump. This in my prop tanks. I'm also experimenting with calcium gluconate in a liverock culturing tank. I hd to put snails in teh tank though, to stop algae. The rock was from an old tank, so I'm not sure if the algae was from nutrients in the rock or the gluconate. I'll have to try again using homemade rock.

[tdwyatt]

IIRC, sodium carbonate over time as a solution will convert to a sodium BIcarbonate solution as it hydrolyses in the presence of water, although there is some isoelectric point that the decomposition will reach equilibrium, such that adding a bicarbonate factor should make this a stable buffer solution. Keeping a stock solution requires an expiration date, although I have no idea when the solution would become inadequate. The half life of the solution would depend on the concentration of the sodium carbonate, the sodium bicarbonate, temp, and the presence (or absence) of catalysts like trace elements. Keeping it under refrigeration prior to use should extend the useful life of the solution, but if it is near saturation, will also cause a precipitatin of solutes. I will try to remember and look in CRC for a half life of the aqueous sodium carbonate/bicarbonate solutions. There is a reason besides shipping weights that washing soda is kept as a dry granular powder.

[Krux]

any harm to premixing the two together and then rehydrating the necessary ammount for each useage? in dry form, will they interract with one another?

[yardboy]

Could you ever keep them in a dry form? Every time you opened a sealed container moisture-laden air would get inside, with the potential of forming a cake of calcium carbonate.

[tdwyatt]

Originally Posted by yardboy

Could you ever keep them in a dry form? Every time you opened a sealed container moisture-laden air would get inside, with the potential of forming a cake of calcium carbonate.

yup, this is the crux of the problem with mixing the dry ingredients. They are so hygroscopic that they will form a calcium carbonate crust on top of the granules every time you open the container. This is what the primary cause of both crusting of ASW mixes and the precipitate that forms in the bottom of newly mixed ASW. Once the CaCO3 forms on the surface of the salt, it will have a VERY low solubility once hydrated, usually collecting as an undissolved layer in the bottom of the mixing vessel.

Randy has been experimenting with a calcium chloride bulk salt mix (used for melting street ice) that is fairly high quality with few impurities for the calcium source, and plain sodium bicarbonate for the alkalinity additive, although the use of washing soda in the mix will stabilize the solution a good bit. Still best to stay as a two part additive, and better yet to mix enough of the powders into an additive solution with the intent of using all you make within a month.

[PaintGuru]

Thats why I like my CaCl better .

[Steve-O]

I use 1/2tsp once a week or so of A&H baking soda to bump up the ph in my FW tank.

[tdwyatt]

Originally Posted by Steve-O

I use 1/2tsp once a week or so of A&H baking soda to bump up the ph in my FW tank.

This may help plants in FW systems, but a different issue in SW systems. It is a misconception to think of adding bicarb to a tank as a means to "bump up" the pH. What actually happens is that you increase the alkalinity/buffer capacity of the system, resulting in the activity of the buffer system being boosted.

If pH is low (like 7.9 or so), it is true that it will bring the pH back to 8.2, but this is not because we added the bicarb specifically, as the bicarb is not necessarily going to increase pH. It is the addition of the bicarb that then boosts the buffer capacity of the water column, that increases the buffer systems ability to resist changes from a pH of 8.2 under home aquaria conditions. Try adding some bicarb to a tank with a pH meter and watch the effect over a few hours.

If the pH is very high (like 8.5 or more), additions of bicarb will bring the pH down, but at the cost of adding loads of sodium to the water column. Additions of bicarb to high pH systems results in the buffer system shifting to the right of the Le Chatelier's equation to release protons and form CaCO3 (this is why you see some CaCO3 precipitate when initially adding alkalinity boosters to the water column.) Much more complex than the simple statement made here, but that is the gist of it. Boosting alkalinity is increasing the capacity of the seawater's buffer system to resist changes from a pH of 8.2 at ~80F and surface conditions in seawater of appropriate conservative element composition and salinity @ 35 PPT. Increasing the bicarb concentration over the ability of the buffer capacity to take more bicarb (and exceeding solubility) can result in the formation of CO2 gas that will bubble off in areas of appropriate surface exchange. Although this will result in a drop in pH, the end result is that the buffer system will be saturated. The issue of what is dropping the system pH has not been addressed, in particular in the absence of appropriate Ca supplementation at the same time.

The buffer system is used up for both the purpose of buffering the water column AND to supply the components necessary for calcification and skeletalization. We should be supplementing these substances to provide for the amounts taken from the water column to make coral skeleton, not to boost pH. Over time, the use of Bicarb supplements and CaCl2 for this purpose ultimately will skew the composition and proportion of the conservative elements, making it difficult to reach high supersaturation levels in closed systems for Ca and alk. Frequent 10% weekly to biweekly water changes reduce this effect, but it will still occur, requiring a once every 6 month's large (~50%) water change to restore the proportionality of the conservative elements to that of NSW.

Ultimately in such a scenario, the salinity becomes a product of primarily sodium and chloride that are left behind when Ca and Bicarb are either spent to supply the buffer capacity for acid/base reactions, or for the formation of skeletons for the corals. Preferably, we would be supplementing these substances to make up for the amounts used in the biogeological reef building purposes (coral skeletons), rather than driving up low pH that may be due to unrelated causes (like high pCO2 inside atmospherically tight houses...)

If a system is suffering from excessive acid production, it is either due to the production of organic acids (like those that result from organic carbon decay) or the presence of excessive CO2. Many threads here that discuss the causes and resolution of these acid production issues. It is better to address the cause of the low pH rather than to treat the symptoms with the bicarb.

Not a flame, just a concerned statement.

HTH

[Jimbo]

Wow Tom that was a great summary. I was aware of that cloride would build up from frequent use of calcium cloride. But you spell it out so well . I was putting in calcium cloride and buffer into my auto-top-off system, but may just start adding kalk paste instead, at least until I can afford a calcium reactor.

I have a question for you. I've read thaty kalk can increase carbonate hardness and in other places have read this is a short term affect and it will only raise calcium long term. I was wondering if you could supply some clarity here.

[tdwyatt]

Originally Posted by Jimbo

...I've read that kalk can increase carbonate hardness and in other places have read this is a short term effect and it will only raise calcium long term. I was wondering if you could supply some clarity here.

If the aquarium has hermatypic corals that are consuming calcium and bicarbonate in equimolar amounts, then the addition of any supplement that will provide these substances will be used up, and the result will be only a short term increase based on a single dose. The use of kalk boils down to finding ways to increase the evaporation rate so that the maximum amount of kalk can be infused continuously over a 24 hour period. whether the amount of calk you are providing will be able to keep up with the demand will depend on the rate of consumption by the corals and the number of hermatypic corals and other calcium/bicarbonate consumers.

Some folks think that because calcium hydroxide (kalk, Ca(OH)2 ) does not have any inorganic carbon (as either carbonate or as bicarbonate), that it cannot be supplying alkalinity in the form of carbonate hardness, but this overlooks the fact that the use of kalk as a source of hydroxyl ions in the presence of calcium ions will preferentially drive dissolved CO2 to form the bicarbonate molecule. Keep in mind that pCO2atmospheric is in almost instantaneous equilibrium with pCO2seawater, such that unless the air above a tank is devoid of CO2, the water column will have a continuous supply of 350 to 450 PPM CO2, depending on the concentration of CO2 in the in-house environment of the water column. In modern closed structures, efficiency for air infiltration is so good that homes with gas logs, stoves, or just plain day-to-day habitation by animals (humans) will drive pCO2 to the 400-450 range. This can affect the early morning pH nadir of the tank (remember that pH in seawater is a direct function of the amount of CO2 dissolved in the water) so much so that values of 7.9 or lower may occur. The use of Kalk will directly drive the conversion of this dissolved CO2 into alkalinity buffer HCO3- ions. This conversion is semi-molar with hydroxide ions, which are provided at a 2:1 ratio to the calcium ion in Kalkwasser powder. The reaction occurs in such a way that alkalinity is provided at equimolar amounts to the calcium to expand the buffer capacity of the water column (and produces a molecule of water that consumes the extra hydroxyl ion). The net effect is that both calcium and bicarbonate are supplemented in equimolar amounts so long as the Kalk drip is continued. No need to add vinegar, although the use of vinegar will dissolve any newly formed CaCO3 precipitate that forms in the Kalkwasser container (this is unnecessary and a bit wasteful, also supplies unnecessary nutrients from the vinegar in the form of organic acids to the tank, when we wish to LIMIT inputs)

Too late tonight to get into the mechanics of the reasons for this, but IF I GET OUT OF BED EARLY TOMORROW, I will work on showing you folks the chemistry as well...

















...but don't hold yer breath...

[davidc]

I didn't understand a lot of what you said Maybe I should just go to college one of these days.

I would like to hear more about why vinegar is not useful. Isn't the whole point of the vinegar to make the Ca(OH)2 easier to workwith, by preventing precipitation and allowing it to be added more quickly? Sounds like you are saying it's better to just drip slowly and constantly and ignore any precipitation. Does adding vinegar reduce the effectiveness of it?

What is your opinion of the 'kalk slurry' method?

Does anyone want to translate into high-school-level chemistry, or provide links where I can learn more about chemistry? I'm glad we can have advanced discussions here I like to know whats really going on in there.