# Ph vs Calcium Deposite on Plants



## zozo (19 Jul 2016)

Hi, i got something intresting going on in my low tech tank i'm rather curious about and wonder if their as more scientific data to be found about the process.

My water parameters are moderately soft kH is a stable +/- 6 from the tap.
The gH changes from time to time and fluctuates from 6 to 12, not drasticaly but year ago i had gH 6 and last fe months i measure a stable gH 11..
My tap waters pH is relatively high end range of 7 from the tap, if the water is depleted after a few days it rests slightly around pH 8.

In the tank with plants and live stock in both low tech tanks it stabilizes at pH 8.5 tops and drops at night to pH 8.2 to gradualy rises to 8.5 during the day. All in all at the high side and very low on co2. I'm not in the danger zone, all fish take it very well and are very healthy, plants just grow slow.. I do not want to add any chemicals to lower the ph nor do i want to use peat, actualy just do not like to force Ph it just needs time to lower naturaly, so i wait patiently for the tank to mature propperly and go down on it's own.

The thing is i wonder about is this calcium deposit on plants with a rather high metabolism.. Caused by a high ph that i know so far.. I my case the only high metabolism plant life in the tank is Algae.. Now i have algae growing in the rocks and a little bit on the wood, which actualy only contributes to the looks, makes a tank looks more aged and can look nice. But now i see calcium deposit form on this algae, the algae gets encrusted with a yellowish, white crust.. On the wood i can remove it with a rasor blade.. But some rocks, not all, it probably must be a certain kind of algae growing there susceptible to it more than others. Dunno but  it's the same rock all over.  Anyway this deposit is rather resilient, it doesn't come off with brushing and with scratching you see it powder up like calcium deposit does on everyting.

Had some old anubias leaves covered with this stuff because they where covered with algae. New growth is not affected and got the algae growth on plants relatively gone. The rest of the plants grow slow enough not to be affected by this process..

Here is an example pic.. A pile of the same rocks all have algae on them and only one, the left lighter colered has this deposit. 





Not that it bothers me so much, i can get used to it, the color aint that bad and guess the encrusted algae is dead and killed in the process.. Funny process actualy, algae growing itself to death in higher pH.  Snails might use it to get building blocks for their shell.

Now i was wondering does this calcium layer disolves again if in time the water acidity lowers again. Might need another 8 months patience for that.. Are there peopel having experienced simular processes in their tank and how did that turn out on the long run??


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## Finn (19 Jul 2016)

Interesting thought regarding the metabolism and limescale build up, perhaps there is a chemical reaction within the algae and biofilm which is producing calcium as a waste product? Or maybe dead cells solidifying over time?  

Anyway, I think it would dissolve fast enough in moderately acidic water, though I can't say I've experienced it myself.

One thing I have noticed though is that my tank with a sand only substrate consistently gets limescale build up on the waterline, while my aquasoil tanks don't at all, presumably because of the buffering capacity of the aquasoil has kept acidity to a point where the limescale could never develop. A benefit of aquasoil (and acidic tanks) that I hadn't considered before.


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## zozo (19 Jul 2016)

It is very common indicator for pond owners.. Calcium deposit on fast growing plants = Check if pH isn't to high.. Because i have such a rather high pH i notice it also in my pond when i place the pondweed (Potamogeton perfoliatus) in a high light spot, it forms calcium deposit on it's leaves. This year i shaded it with lots of floating vegitation and it stays clean. I know @dw1305  wrote something about it somewhere a while ago but i can't seem to find it back.

Now for the first time i experience it in the fishtank with algae on rock and wood.


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## rebel (20 Jul 2016)

Is it a case of biiogenic de calcification ?

http://www.thekrib.com/Plants/CO2/decalcification.html


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## zozo (20 Jul 2016)

rebel said:


> Is it a case of biiogenic de calcification ?
> 
> http://www.thekrib.com/Plants/CO2/decalcification.html



I guess that is it, thanks for looking into it Rebel, i couldn't find the English terms for it to do a proper search. 
Intersting to see algae do this and cover hardware completely with a layer of calcium deposite.


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## rebel (20 Jul 2016)

Can you break something off and put it in vinegar...Does it bubble?


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## zozo (20 Jul 2016)

it doesn't form chunks big enough to break off.. But if i scratch it with something hard i see it come off a bit dusty and like powder. I didn't try, have a few rock with this stuff on it i could take one out an try.. The most rocks i can take out i already did clean while back from algae before forming this, those i used as soil retainer i left in place i might dig up some plants if i pull them out of the substrate, i rather take it for granted..  It's a calcium/magnisium deposite alright, what else can it be, the sum adds up. So it probably will fizz off in vinegar..

I wondered if more people have this, but i guess since low tech became a bit out of (old) fashion.. The chances finding some with low tech and also in the higher ph range are rather slim.


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## rebel (20 Jul 2016)

If it fizzes, it won't prove calcium but CO3 more likely.  

But I agree with you though likely to be Calcium CO3.


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## zozo (20 Jul 2016)

I resently scratched all off the wood during a cleaning session.. If i see it form again i try to chip something off and see what it does. For the rocks it is on, i'm not going to take chances, they holding the slope together and pieces of wood are resting on it.. The one in the pic above is 3/4 of it's volume bellow the substrate. Or i just wait till it forms on a rock i  can take out, but i'm afraid i have to algae growth to much under controll now..  (I hope)


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## rebel (20 Jul 2016)

you can lower the water level and pour some vinegar on it...   Kidding.... (but perhaps not)
Then just refill with the same water.


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## rebel (20 Jul 2016)

Also if you add some peat to slowly lower the kH, pH, then it would be interesting to see what it does.


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## zozo (20 Jul 2016)

That's the point, i do not want to mess with the pH and kH..  I've used inert substrate, so it will take some time to get it going, but i guess if my bacteria cycle slowly optimizes it'll lower the pH as well.. Tank is only 8 months old, not yet much goin on in the substrate, to i slowly see all crypts finaly taking off into it.. And actualy i'm glad i got my wood now to stop leaching and staining the water, so adding peat i'm back to square one.. Tho i did put soem peat in the substrate where i planted rooting plants.. But that's far to less to have effect on the total  water column. 

It is i'm not in trouble, tank is doing great, as far as low tech goes it's doing alright..


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## rebel (20 Jul 2016)

Interesting. I used to have a very high kH due to adding a wrong amount of calcium carbonate pebbles to a DIY sub. Over 2 years this has settled down completely to a kH of 4. I guess the plants just gobbled it up. My tap water is kH 4 with pH 7.6 (limed).


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## zozo (20 Jul 2016)

My values are rock steady, fortunately and i rather keep it like that and do not make manual alterations, i do not have positive experiences with it. et do nature it's cause is much more steady and safe.. Hence t is low tech slow burner, so why mess around with it.. Have enough work and messing around as is in the high tech.Finaly got that one steady and took me over a year.  Got another low tech setup with even lower light completely different hardscape materials and has the same values, that's how i know it's not in the used materials, it's from the tap water.


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## dw1305 (20 Jul 2016)

Hi all,





zozo said:


> but i can't seem to find it back


Probably in <"pH increase...">. The "biogenic decalcification" link Rebel posted has a good explanation.





zozo said:


> Now i was wondering does this calcium layer disolves again if in time the water acidity lowers again.


Yes it should. As you add acids (H+ ion donors), insoluble CaCO3 will be converted to soluble HCO3-. 





zozo said:


> In the tank with plants and live stock in both low tech tanks it stabilizes at pH 8.5 tops and drops at night to pH 8.2 to gradually rises to 8.5 during the day.


The pH8.2 is the pH you get when carbonate buffered water (as HCO3-) is in equilibrium with atmospheric CO2 levels (~400ppm CO2). The water has a reserve ("buffer") of CO3-- ions and is fully saturated with HCO3- ions. If the water warms, or the volume drops, it can't hold as much CO2 and you get the least soluble carbonate (CaCO3) come out of solution (this is why you get a "tide mark" at the water level).

You also get the same effect if you add a more soluble monovalent carbonate (via the common ion effect). When you add NaHCO3, to carbonate buffered tank water, the fine white powder deposited is CaCO3 coming out of solution.

In biogenic decalcification the plants remove CO2 (often from the HCO3- ion) during photosynthesis raising the pH (O-H is a base) and deposit CaCO3 on the leaf surface.

The pH can potentially rise to very high levels in water where you have rapid photosynthesis (with a large volume of plants capable of utilising HCO3-), because of the high levels of dissolved oxygen and added OH- ions. If you have a deep tank, with a small gas exchange surface area (via low water turn-over), this is exacerbated by slow diffusion of CO2 in to, and O2 out of, the water.

cheers Darrel


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## zozo (20 Jul 2016)

dw1305 said:


> Probably in <"pH increase...">.



Yes, thanks Darrel, that one and another topic with someone asking wath this deposit was on its Anubias leaves, he tought it was algae.. . But the one you link to you indeed go into a lot deeper. Have to read it all over again.. Have some very nice Elodea growth in th egarden this year, so beautifull bright green i had to put some in this tank. Both have same parameters anyway. See what it does in the pond it is spot on clean and very lush.. See if it will deposit CaCO3 in the tank or does some with the ph.

Besides Elodea actualy can be a very beautiful plant, always wonder this plant has so many different grow forms under different conditions.


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## Manuel Arias (19 Aug 2016)

Hi there,



dw1305 said:


> Yes it should. As you add acids (H+ ion donors), insoluble CaCO3 will be converted to soluble HCO3-.



Darrel is right, but only if pH gets below 8.2. Otherwise you will not see improvement in this line. The reason is that above 8.2, the fraction of CO2 species in form of dissolved gas is zero, which means the plants (or algae) are using the bicarbonates instead, what explains the precipitation of calcium carbonate observed by Zozo.

Cheers,

Manuel


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## zozo (19 Aug 2016)

Manuel Arias said:


> Hi there,
> 
> 
> 
> ...



I red at several articles that generaly the fast growing plants are affected.. I took it to the test and threw in a handfull of Elodea a month ago.. It grew 200% by now but is as clean as it can be. I'm not so sure if it realy is the plant doing that but more likely algae, in my case it only is algae doing this.. And the case where anubias leaves where covered, i'm pretty sure it was the algae as well wich covered the anubias leaves first.  At the time all anubias leaves are relatively clean of algae and the do not develop this calcium carbonate layer.


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## Manuel Arias (19 Aug 2016)

zozo said:


> I red at several articles that generaly the fast growing plants are affected.. I took it to the test and threw in a handfull of Elodea a month ago.. It grew 200% by now but is as clean as it can be. I'm not so sure if it realy is the plant doing that but more likely algae, in my case it only is algae doing this.. And the case where anubias leaves where covered, i'm pretty sure it was the algae as well wich covered the anubias leaves first.  At the time all anubias leaves are relatively clean of algae and the do not develop this calcium carbonate layer.



You are right, Zozo. I agree that is likely to be the algae, even when happens over the leaves of the plants.

The reason why is because there are three strategies for plants making use of bicarbonates when CO2 availability is poor or non-existing:

1. Proton extrusion: Essentially, the plant/algae pumps protons to the boundary layer, changing pH locally, and then favoring the formation of CO2 in form of dissolved gas. The CO2 so formed is then absorbed.
2. HCO3- absorption: The plant/algae pumps bicarbonates inside the cells. Then carbon anhydrase enzyme removes ions OH-, who are pumped outside the cell. This OH- pumping increases locally the pH int eh boundary layer, what favors the formation of carbonates, who usually link to calcium, and then forming such precipitate.
3. External carbon anhydrase: The plant/algae have the enzyme in direct contact with water. The transformation of bicarbonate into CO2 and OH- happens then in the boundary layer, and CO2 is absorbed. The process increases the pH with the same effect than above.

You can read about this <here>.

Plants tend to favor proton extrusion, which requires pumping sodium inside the plant. Some of them, however, use the method 2, but is more expensive in terms of photosynthesis efficiency, as it requires active pumping of OH- from cell to exterior, whne pH outside is larger than inside, so has to be forced.

Algae, however, tend to use the last option, because is simpler, but less efficient in terms of generating CO2. The advantage is that does not involve osmotic changes and require less energy too.

Cheers,

Manuel


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