Nerite Snails in high tech

[dw1305]

Hi all,

I understand the chemical reactions one by one but not as a whole picture inside the tank in addition to everything else. Are you saying that when you add CO2 all of the Ca++ are exhausted?

The calcium is still there, either combined into a (largely) insoluble compound (often CaCO3, but most calcium compounds aren't very soluble) or as an ion (Ca++). The carbon (C) is slightly different, it can be a solid (CaCO3), in solution (HCO3-, 2HCO3) or as a gas (CO2).

The reason that calcium carbonate is such a useful compound for organisms (and has build up into huge biogenic rock layers over the last 3 billion years) is really the equilibria between CO2 ~ HCO3 ~ CaCO3.

The problem for the mollusc shell is that if you add an acid (H+ ion donor), CaCO3 will be converted into ions

2 H+(aq) + CaCO3(s) --> Ca++(aq) + H2O(l) + CO2(g)

and even when the ions are re-deposited as insoluble CaCO3, they won't be re-deposited in the same place.

This means that the older shell will degrade over time.

The rate of degradation will depend upon the excess of H+ ions, and we can estimate this from the pH (the ratio of H+ ion donors : H+ ion acceptors), the lower the pH ("greater the excess of H+ ion donors") the more quickly the shells will degrade.

If you always have an excess of H+ ion acceptors, ("base-rich" conditions like Lake Tanganyika) the calcium carbonate will never dissolve and huge Neothauma shell beds (below), can develop

<http://seaframes.wordpress.com/2012/07/16/home-shelly-home/>.

The problem for us is if we take a mollusc which has evolved in hard alkaline water and place it in soft water it won't have any of the physiological adaptations to softer water. This is why you get a limited number of slow growing molluscs in acid waters.

cheers Darrel

 

[sciencefiction]

If you always have an excess of H+ ion acceptors,

Aren't there more H+ acceptors in a fish tank? Why would the H+ always go for the CaCO3 only and not lets say for some other base if available and thus spread the load of the acid conditions?
As I mentioned on another thread my snails had eroded snail shells in a Gh of 14, no co2 added at all, but no water changes for a while done and it seems to me the Ca++ were all exhausted and not in the form of Ca++ anymore or despite my ph of 7.4 I had loads of H+ attacking the CaCO3 of the snails.

 

[dw1305]

Hi all,

Why would the H+ always go for the CaCO3 only and not lets say for some other base if available and thus spread the load of the acid conditions?

Chemistry doesn't really work like that, the solubility of ions is dependent upon their position on the periodic table and their valency.

For example if you add enough sodium bicarbonate (Na2HCO3) to a solution containing Ca++ and HCO3- ions, you will always get CaCO3 precipitate out, because CaCO3 is much less soluble Na2HCO3. This is the <"common-ion effect">, and how ion exchange water softeners work.

As I mentioned on another thread my snails had eroded snail shells in a Gh of 14, no co2 added at all, but no water changes for a while done and it seems to me the Ca++ were all exhausted and not in the form of Ca++ anymore or despite my ph of 7.4

I'd look at it another way, if you have shell erosion you know that you have times when the pH is below pH7, the shell erosion is the "smoking gun".

Have a look at "Old Tank Syndrome" - <http://www.skepticalaquarist.com/bioacidification>.

cheers Darrel

 

[sciencefiction]

I'd look at it another way, if you have shell erosion you know that you have times when the pH is below pH7, the shell erosion is the "smoking gun".

Mmm, and what causes the ph to go back up exactly when I test it? The Kh was never below 5, from original 8 so the ph did have enough buffers.

 

[dw1305]

Hi all,

Mmm, and what causes the ph to go back up exactly when I test it? The Kh was never below 5, from original 8 so the ph did have enough buffers.

You need to take whatever approach you are happiest with. A lot of successful aquarists are fanatical water testers, but personally I very rarely test any of the parameters in the tanks.

I just use visual clues to give me an idea of when to add fertiliser ("Duckweed Index") or clean the filter (reduced venturi bubbles), or add a bit more tap water (severe snail shell erosion, our tap water is about 17dKH and 500 microS) to my rain-water for water changes.

The reasons for this are that I'm a pretty lazy tank keeper and these are KISS solutions which I've arrived at over time, based upon both my experience as a tank keeper and my day job.

For me the 3 parameters I'm really interested in for any fish keeper are

• "Do you have plants?" if they don't keep planted tanks, I try and persuade them that actively growing plants are the single factor that makes tank management and maintenance of water quality easier.
• "What type of filtration do you have? and what filter material is in it?" Again if they can have a "wet and dry trickle filter" I tell them that it is the gold standard, it is a simple and robust solution to biological filtration. If they have a canister filter I talk more about flow and oxygen.
• "Biochemical Oxygen Demand" bit of a strange one, because you can't measure it, but this is what plants and filtration parameters are really all about, reducing BOD. At the most basic level a successful tank is one where the amount of dissolved oxygen in the water column always exceeds the BOD. Assuming you feed your fish, realistically everything else is froth.

I'm in an extremely privileged position in that I have access to a lab with several 100K's of analytical kit in it, but even with that resource there are plenty of tank issues that wouldn't be detectable.

Your eyes can tell you more than any analytical kit ever will.

cheers Darrel

 

[sciencefiction]

But that's exactly my point, one can't rely on tests to show them the conditions in the tank as it seems whatever tests we use are just useless of giving you the big picture.
I tested only out of curiosity to see in what directions the stats change over period of time without water changes. I've never ever relied on tests to show me if the conditions in the tank are good for plants or fish but it doesn't stop me from testing to see what those commercial tests are happening to show for one or another reason.
The Gh went from 12 to 14. The Kh went down from 8 to 5. The Ph remained unaffected at 7.4 all the time. Yet, with these stats I get eroded snail shells in just one out of 2 tanks treated the same way for a period of time. However, the other unaffected tank has dolomite(CaMg(CO3)2) under the substrate which as far as I know dissolves very slowly.
In the problem tank all snails were affected, mts, ramshorns and pond snails to various degrees so it wasn't just one species. The substrate differs too, the affected tank has sand the unaffected soil capped with sand(dolomite and potassium chloride under the substrate)[DOUBLEPOST=1404826567][/DOUBLEPOST]

Have a look at "Old Tank Syndrome" - <http://www.skepticalaquarist.com/bioacidification>.

I've read this one a couple of times before. I am aware of what happens, hence I've tried to monitor if it indeed happens when one neglects a tank. For the last year or so I specifically neglected tanks for the first time and in none of them the ph dropped or even moved one point, keeping in mind that my tap water is naturally hard so it would take longer for that to happen. The Kh does go down but very very slowly so yes, one day the ph may have dropped if I left the tanks longer like that but I think that unless one has very soft water, there's enough buffers even from fish food added so the effect is really not that easy to cause.

But the only time I had "old tank syndrome" was not in non-water change tank but in a fry tank with heavy water changes but heavy feedings several times daily. The ph plummeted down quicky and fish were visibly affected which was why I noticed.

 

[frothhelmet]

I tried keeping freshwater nerites (Theodoxus Fluviatilis) initially in ph 6.5-ish water, but the pitting in the shells from the acid water eventually kills them (takes a couple months). When I raised the Ph over 7 they stopped dying and started breeding.

 

[andy-mu]

All acids are "H+ ion donors", and as you add H+ ions, the H2CO3 is formed (from CaCO3 going into solution). Any excess CO2 is evolved as gas.

I'll use hydrochloric (HCl) as my acid, (but the process is the same for any H+ ion donor): HCl makes it simple to understand, because you can just ignore the chlorine ion (Cl-):

You need "2H+" to make the equation balance due to the different valencies of the ions. (s = "solid", g = "gas", l = "liquid", aq = "in solution")

2H+(aq) + 2 Cl-(aq) + CaCO3(s) --> Ca++(aq) + 2 Cl-(aq) + H2O(l) + CO2(g)
discard the balanced chlorine ions and you get:

2 H+(aq) + CaCO3(s) --> Ca++(aq) + H2O(l) + CO2(g)

Wooah. Waaayyy too heavy for me. Chemistry aint my thang. Think in layman terms Nerites aren't perhaps suited to C02 injected planted tanks 🙂

Comprehensive as I'm sure your reply is Darrell, I know when I'm out of my league. Chemistry for me gets as good as, add hydrogen peroxide to water with the filter off and you get loads of oxygen bubbles and kill BGA as a spot dose. Fun to watch and somebody told me it was okay to do it. Just as well people like you are here.

 

[dw1305]

Hi all,

Nerites aren't perhaps suited to C02 injected planted tanks

I think that's probably the bottom line.

Wooah. Waaayyy too heavy for me

Get away with you, it isn't really chemistry.

Once you start injecting CO2 etc. you need to understand what you are doing, mainly because when things go wrong it allows you to have an educated guess how to put it right.

cheers Darrel

.

 

[sciencefiction]

Is it because of the CO2 being unbearable rather than the drop in Ph because I have a friend with a tank with a Ph ranging from 5.5 to 6 and unreadable Kh and the nerites have been perfectly happy.

 

[Sacha]

Is the answer simply that no- one knows?

 

[dw1305]

Hi all,

Is it because of the CO2 being unbearable rather than the drop in Ph because I have a friend with a tank with a Ph ranging from 5.5 to 6 and unreadable Kh and the nerites have been perfectly happy.

I've never used CO2, so I can't pass comment on that bit, and they may be the readings his test kits give, but I'd be surprised if they are the actual tank water readings.

I think once you are below pH7 shell erosion will occur even if the snails are eating a calcium rich diet. The shell is made of biogenic "aragonite" CaCO3, so once you are below pH7 the shell is going to erode once it is away from the area of active shell growth, even in snails that can live in acidic water. Nerites have quite thick shells, so it may take some time for obvious shell erosion to occur.

Because pH is a measure of the ratio of acids (H+ donors):bases(H+ ion acceptors), an acid pH of below neutral (pH7) indicates you have more H+ ion donors than acceptors.

At pH6 you have 10x more H+ ion donors and at pH5 x100. So anywhere below pH7 you have this situation:

The problem for the mollusc shell is that if you add an acid (H+ ion donor), CaCO3 will be converted in to ions:
2 H+(aq) + CaCO3(s) --> Ca++(aq) + H2O(l) + CO2(g)
and even when the ions are re-deposited as insoluble CaCO3, they won't be re-deposited in the same place.

And the same applies to 0dKH, carbonate will lost from the older bits of the mantle, we know this because of the HCO3- ~ CO2 equilibrium.

All the time the pH is below pH7 available insoluble sources of carbonate will be converted to bicarbonate ions (HCO3-), and this will continue until equilibrium is reached. As the shell goes into solution both pH and dKH will increase. Even if the dKH/pH then rises due to the addition of a more soluble carbonate source (like NaHCO3) the CaCO3 won't be re-deposited on the shell.

As soon as the soluble NaHCO3 (as Na+ and HCO3-) is depleted we're back at 0dKH (there is no reserve of buffering in this case because NaHCO3 is highly soluble), and shell erosion will re-occur.

cheers Darrel

 

[Mick.Dk]

- and this is why I have a separate tank for breading ramshorns - pH 7.5 - 8.0.
Most tanks at Tropica are run on pH around 6.8, but I'm a sworn believer of benefits from keeping ramshorns in a tank. As seen from this thread, the ramshorns don't thrive long-time, though, and need to be re-introduced !!
- You just can't bend the rules of chemistry, basically..........

 

[andy-mu]

As the rolling stones once sang.....You cant always get what you want.

I'm at the re-scape planning stage. I would like nerite's and Sulawesi shrimp. Aint gonna happen with the type of PH I'll be running.
I do plan on C02 injection, T5's. Hopefully do it right this time. Get the flow and distribution sorted.

I take it basically all snails will suffer in the C02 injected planted tank?

 

[dw1305]

Hi all,

I take it basically all snails will suffer in the C02 injected planted tank?

You'll need some-one who uses CO2 to give you a definitive answer. My suspicion would be that if your water was hard and alkaline (both dGH & dKH high) you wouldn't particularly have any problem in the short term, although older shell whorls will degrade.

During CO2 injection the pH may fall below pH7, but you haven't actually changed the water chemistry, you've just added more CO2 and driven the HCO3-~CO2 equilibrium towards CO2 (really towards the small proportion of CO2 that has become carbonic acid H2CO3). As soon as you stop adding CO2 the pH will rise as the HCO3-~CO2 equilibrium reverts to atmospheric CO2 levels.

Shell erosion will still occur during the periods when you add CO2, but these will be no more than 12 hours and followed by a period of hard water when shell can be built. Away from the shell mantle, (where active shell formation is occurring) erosion will occur whilst the CO2 is on.

cheers Darrel

 

[tim]

I've had a few hitch hike on plants etc, London tap water (hard water) co2 tanks they never last long, generally they just don't grow.

 

[sciencefiction]

but I'd be surprised if they are the actual tank water readings.

The tests used are liquid tests JBL for Ph showing 5.5, API ph doesn't go below 6, shows 6(yellow on the chart)
KH for both 0-1.
Water coming out of the tap is naturally very soft, I am not doubting the tests by much but not tested with digital Ph meter.
Owner also has Malaysian trumpets in the tank too doing just fine.
Tank is low tech, no CO2 added.
Oh, and I forgot to mention, owner had an Apple snail who had shell erosion so it seems it may depend on snail species who does well in low ph and who doesn't. Snail was given away.
The nerites are a couple of zebra nerites, about 1-2 years old, still alive and no shell erosion whatsoever

 

[dw1305]

Hi all,

The nerites are a couple of zebra nerites, about 1-2 years old, still alive and no shell erosion whatsoever

Interesting, there is definitely something strange going on.

I'm pretty sure that in one of the other "low tech" snail threads there are pictures of a healthy Zebra Nerite in a tank with CO2 injection. Hopefully some-one reading this thread will be the owner and be able to offer some more details.

cheers Darrel

 

[Sacha]

My nerite snail is healthy enough, but I only see him during the Co2- off period. It's about 3-4 years old, and has been in this tank happily for this time. The pH drops to around 6.2- 6.4, the KH is 2-3.

 

[dw1305]

Hi all,

My nerite snail is healthy enough, but I only see him during the Co2- off period.

Does it crawl above the water line during CO2 injection? That could account for why it is still doing well.

cheers Darrel