the chemistry doesn't make sense......

[mgkaelen]

i made a post a while ago about crushed coral being used as a natural pH up, and tried to read all the posts i could about it. what i read was that the crushed coral acts as a buffer to the acid;
a buffer doesn't change pH though, it just makes pH more STABLE --- much more difficult to CHANGE the pH once you have a buffer. so if my pH is LOW, wouldn't i want to get it up somehow, THEN use the coral to KEEP it that way? a guy at the LFS today (i don't trust any of those guys) said that i would need the coral AND a buffer-- did he mean instead of buffer that i'd need something like pH UP? i know i don't need a chemical to do this, i 'm just confused of the actual proces sthat takes place.

ALSO,
i read that you're supposed to add a TINY bit of coral (1/2 tsp per every 10 litres? did i mis-read)? when i went to the LFS today, they only sold 10lb bags of the crushed coral and i know i only need about a handful. when i told the guys that worked there that, they said "well what about adding a coral"; which reminded me! i have this coral that my boyfriend's mom dug out of the ocean about 9 months ago and gave to us and it's been sitting on my bookshelf ever since since i have no idea what to do with it. i've cleaned it out -- could i use THIS as my carbonate source? if so, will the entire coral be too much and change the pH dramatically? the coral is about 5 inches x 4 inches to give a rough estimate.

anyhow, any help to bring to light HOW this buffer works and the ORDER in which to add it all to my tank would be much appreciated. thanks guysssssssssssssssssss.

oh by the way, other tank params are great. KH isn't tested at my LFS but i checked my city's KH and i believe it's 104 which someone told me was a good KH and the crushed coral would work well with that number. thanks![/u]

 

[mgkaelen]

oh yeah, pH in my tanks are 6.5 and 5.0; have been that way for quite sometime so i know the fish are fine, but i'd like to add more fish sometime and don't want to kill them due to shock. the 5.0 pH is in my 10g planted tank and i turned off the CO2 a while ago since i know that works as a pH down.

 

[poikilotherm]

A buffer doesn't just make the pH more stable. It makes it stable at a particular pH depending on the buffering system. Carbonate buffers buffer best at pH's between 8 and 10, but harden water. Phosphate buffers work in the 6.5-8 pH range, but introduce algae growth problems. That KH translates to about 6 dKH, moderately soft. Coral should raise pH and buffer simultaneously, don't worry about adjusting the pH first.

The amount that the coral affects the water will depend primarily on surface area of the coral, so I imagine that your chunk of coral will dissolve pretty slowly, and be OK to use. Boil it for a while first, just to be safe. Just monitor your pH, GH and KH.

Buffers are pretty complex unless you have a background in chemistry, but there are many references on water chemistry such as:
http://faq.thekrib.com/begin-chem.html

 

[TankGirl]

Let me just relay my personal experience with crushed coral, and that might help you. I started an African cichlid tank years ago with water out of the tap measuring about 7.4 pH and KH of about 5 degrees, GH of about 10 degrees.

I put buffering sand in the tank and petrified coral rock, and did not see a very noticeable increase in pH, alkalinity or hardness. I then got a giant bag of crushed coral (probably the same bag I am using now) and put about a cup of it in my filter. In about 3 days I had pH up to 8.2, KH up to 7 degrees and GH up to 15 degrees.

I think it would be a wonderful experiment (one that can really do no harm) to add CC to your filter and see what it might do to your pH and your KH.

 

[mgkaelen]

i guess i should get the cc then; i will try the coral that i have and see how it works in a week or so; i have done 3 water changes in 2 weeks with no fluctuation in pH so i'm not in any rush i suppose becuase i know the fish are used to it because at least the pH is stable.

poikilo: i am familiar with chemistry which is why i was confused what was going on. however, you said that the Carbonate buffers work best at a pH of 8-10. is this your aimed pH? because i'll be starting at a 5 & 6.5 pH and trying to get around 8...

 

[poikilotherm]

Crushed coral will increase your pH depending on how much you use. If you use lots and lots, it'll bring it to a rock-solid stable really hard 9ish, but if you use less it'll bring it to a pretty stable, moderate 8ish, which sounds like what you're looking for. Carbonic acid is a weak acid so it buffers to a high pH. No other buffers are necessary. Have fun!

 

[mattrox]

It is not so much the weight, but the surface area. A big lump of coral will not react as quickly as a handfull of crushed coral. Especially if it is in the filter with water rushing all around it.

 

[madasafish]

Let's see if I can help with the Chemistry at all, Kaelen. Stephen, correct me if I'm wrong. Not 100% sure that it's right, but I am 100% sure that I'm giving a simplified version of it, as there are many more steps to all of these reactions than I'm mentioning.

-------------------------------------------------------------------------------------
A basic reaction... the balance of CO2 and pH in water.

H2O + CO2 +... <=> H+ + HCO3- (bicarbonate) + CO3^2- (carbonate) + H20 +....
-------------------------------------------------------------------------------------

CO2 regulates pH in water, as CO2 and water will react, creating H+ ions (the substance of pH--pH is lower when there are more H+ ions in a solution) and bicarbonate and carbonate. (CO2 exists in some quantity in all water, and is always moving in or out of the water due to gas exchange, so the above reaction never goes to only one side.)

H20 is in abundance in this reaction, so rate of reaction this way (->) is determined by the limiting reagant, CO2. Rate of reaction the other way(<-) is limited by the amount of bicarbonate and carbonate in the water. In an environment with more bicarbonate and carbonate, the reaction will proceed faster in the backwards direction, raising the pH.

As I understand it, then, CaCO3 (Calcium Carbonate) acts as a "buffer" in accordance with reaction rates. It is perceived as a buffer because it will react very quickly in acidic environments, and quite slowly (imperceptibly) in higher-pH environments. In other words, it exists in water in a fairly unreactive state unless the pH of the water is fairly low (when the H+ ion concentration is quite high). The ions (Ca^2+ and CO3^2-) will disassociate in water, and the carbonate ion will be able to react with the H+ ion, reducing the number of H+ ions, and keeping the pH up. When there are few H+ ions to react with (high pH), the reaction rate slows, and the pH does not continue to shoot up.

-------------------------------------------------------------------------------------
Something along the lines of...

CaCO3 ---disasocciates in water---> Ca^2+ and CO3^2-

CO3^2- + 2H+ ... --> HCO3- + H+ +...

Then HCO3- + H+ <=> H20 + CO2 +... (all equations unbalanced)
-------------------------------------------------------------------------------------

So, finally, then, in the context of the aquarium...

CaCO3 you add to the water in the form of coral will buffer pH to a certain level because it uses up H+ ions at a particular rate. When H+ ions are more scarce, the pH won't change much, and the CaCO3 will just hang out, and raise to a certain level, as the surface area of the coral reacts with the water. At a certain level, the KH (Carbonate hardness) of the water will become stable. This is the level at which the reaction of the coral and water (CaCO3 + H+ +H2O, the backwards direction) and the reaction of the CO2 and water (CO2 + H2O, the forwards direction) are more or less cancelling each other out. In this way, the first equation comes to a relative equilibrium.

Does that make any sense? It's amateur Chemistry... I'm still learning, but this seems to make sense to me.

 

[aquazen]

All a buffer does is keep the pH from shifting too much. Different buffers work at different levels. Some may raise the pH up to 8 and keep buffering at 8 while others can raise it up to 10 and buffer at that level. Most of the time, it's not so much the amount but the compound that you use. But like all buffers, they are consumable. If you have TOO much acid in the water (enough to totally consume the amount of buffer you have present in solution), there will be a drop in pH. So, that's how it works in a nutshell. Don't get too caught up in crunching the numbers. The principle is the key. Just see that your fish are happy in the pH they're at. Treat the patient, not the numbers.

 

[MarkLehr]

Also, true crushed coral will not begin to buffer until your pH drops below about 7.6 ; you may also have an aragonite based coral gravel which will buffer at much higher levels.
My number 1 rule of fishkeeping is don't mess with pH. You would be much better off to simply find fish which are compatable at the natural pH of your water supply. In all my years I have kept everything you can imagine and i have never found a reason to adjust pH. Your fish will be much happier at a consistant pH which is lower than they prefer, than they will be at levels which are constantly fluctuating.

 

[BrianNY]

There is some excellent information here. I'll take it a step further. The most misunderstood and thus easily abused part of this hobby is in the water chemistry. Too many people test their tap water and think that that's the pH their tank water will remain at. They never understand that there are both chemical and biological dynamics that continually work to alter the pH.

Worse still is that when people read about a fishes requirements, the pH is expressed as some ideal number which they think can be dialed in like the temperature. When they check the pH of their tanks days, weeks, or months later they find the number doesn't match the ideal and rush to buy a product to bring the pH where they think they need it. This usually causes a violent swing in pH which stresses the fish and the pH change is only temporary and very quickly reverts back to what the dynamics of the tank dictate.

I've yet to see the fish that hasn't adapted to a fairly wide range in pH. My discus spawn in a pH as high as 7.8. "The book" says they need a much lower pH. That's simply an untruth. They do just fine as long as the pH is relatively stable. Stable is the key.

IMO, the reason to test pH (in most cases), is to see how much it is fluctuating in a 24 hour period. Fluctuations too quickly are bad. Not to try and find that magic number which can't be dialed in anyway.

 

[workfortheman]

madasafish~ that is some great stuff, really! super simplified aquarium chemistry, I love it! I am currently having pH troubles in my 20 gal with green spotted puffers. I have a couple plants in it (java, anubias, sag) and want to make it liveable for them, so not too high of a pH. I introduced several peices of dead coral (about 8), and they seem to raise the pH VERY slowly. I think I am going to try an experiment: crushed coral in teh filter AND DIY CO2 for the plants. The pH should come to a pretty normal equilibrium then, right (depending on ratios I guess).

Looks like to answer mgkaelen's question, crushed coral DOES increase pH, and tend to keep it there! It will be most effective in high-flow areas, right?

 

[workfortheman]

Also, BrainNY~ what about pH fluctuations caused by photosynthesis in heavily planted tanks? Fish seem to do fine with those. . . .

 

[TankGirl]

The pH fluctuations that occur naturally over time are, in general, very gradual and slow, and allow the fish to adapt to them, so are much less of an issue than when you buy products that immediately alter the pH. I do this all the time with my swimming pool, and they don't call it "Shock" for nothin'!

After years in the hobby you get to a point where you want to start keeping fish that prefer a different pH than what you have out of the tap. Hopefully by then you have an understanding of your tanks and rudimentary water chemistry. My mbuna and peacocks would do fine in my tap water - no adjustments necessary - too true, but their color and spawning behavior is much more true to nature and more interesting with a raised pH and alkalinity. If you are new to the hobby, though, there is absolutely no reason to fool with it.

Two most interesting threads on this subject:

http://aquariumadvice.com/viewtopic.php?t=11464

http://aquariumadvice.com/viewtopic.php?t=19763

 

[jsoong]

Also, BrainNY~ what about pH fluctuations caused by photosynthesis in heavily planted tanks? Fish seem to do fine with those. . . .

I'll take a shot at this one ....

As Madasafish said nicely, the buffers help to hold the pH at a particular level. The "natural" buffer - carbonate/bicarbonate system - will tend to drive the pH towards 7.8 or so. Other buffers (such as phosphates, etc) all have different pKa's & different equlibrium pH's - but as others had said ... you don't want to use these to mess with your pH ... as least not in the beginning.

Anyway, with adaquate buffers present, the pH will not change without something drastic happening. Photosynthesis on its own won't do too much ... any excess H+ will be mopped up by the bicarbonates ... so the pH will be unchanged. <That is the meaning of buffer!> ..... The typical pH crash occurs when you use up all the buffers in the water - but that usually takes months or years and can be avoided by regular water changes (or adding additional crush coral ... etc.)

The only problem with pH in a planted tank may be with addition of CO2. In this case the CO2 is NOT in equlibrium with air, and your pH will change with the CO2 levels in the tank - which will change with the photosysthsis level of the plants. The change should be small, however, if you have adaquate KH (ie. bicarbonates).

 

[mattrox]

The problem with pH levels quoted in books is that they are pH levels of waterways where the species is originally collected. These pH readings are taken at a particular time. I bet the pH in most rivers are not just a single value the whole year, epecially tropical rivers where in the wet season the volume if water changes. This will dilute acids and alkalis. pH=-log[H+]. this relies on concentration which can't ever stay 100% stable in nature.