Ca, Mg and hardness

[gerald]

Soft-water fish must have super-efficient ion-uptake cells in their gills (and intestines?) to get all the Ca and Mg they need from an environment that hardly has any. Since we usually measure total hardness without distinguishing Ca from Mg, I'm wondering whether there's some acceptable range of Ca:Mg ratio they need. Seems like this would be even more critical for soft-water fish than for hard-water fish, where both ions are usually in abundance. Anybody got info on Ca:Mg ratios in natural soft-waters, e.g. S.Amer, W.Africa, SE.Asia ?? I normally use tiny amounts of crushed coral/aragonite gravel in a filter to provide (presumably) both Ca + Mg and weak buffering for soft-water fish after the pH starts to drop (my tap water is about 2 dGH). Just wondering whether Ca/Mg imbalance might be one of the problems folks have with "delicate" species.

 

[tjudy]

Interesting question. I have not thought specifically about Mg and Ca except for my larger cichlids. I use magnesium sulfate (Epsom salts) to help ward off bloat and hole in the head. I have plenty of calcium carbonate around here.

 

[jaafaman]

Soft-water fish must have super-efficient ion-uptake cells in their gills (and intestines?) to get all the Ca and Mg they need from an environment that hardly has any...

It is my understanding that the difference between hard and soft water fish lies more in their ability to shed or retain ions as necessary, and that the majority of soft water fish rely more on ingestion than absorption for nutrient sources.

However,

...Since we usually measure total hardness without distinguishing Ca from Mg, I'm wondering whether there's some acceptable range of Ca:Mg ratio they need. Seems like this would be even more critical for soft-water fish than for hard-water fish, where both ions are usually in abundance. Anybody got info on Ca:Mg ratios in natural soft-waters, e.g. S.Amer, W.Africa, SE.Asia ?? I normally use tiny amounts of crushed coral/aragonite gravel in a filter to provide (presumably) both Ca + Mg and weak buffering for soft-water fish after the pH starts to drop (my tap water is about 2 dGH). Just wondering whether Ca/Mg imbalance might be one of the problems folks have with "delicate" species.

The more common average is around 3:1 Ca:Mg, but sources like Lake Tanganyika turn that ratio completely on its head and the best advice in this instance would be to research the fish's natural chemistry. Some studies, such as this abstract The effect of calcium and magnesium ratios on the toxicity of copper to five aquatic species in freshwater, support the conjecture that "off" ratios of the two can indeed affect the fish's reaction to its environment and ultimately its health.

It is also one of the reasons I try to maintain any mixed-species tank with those from similar, if not the very same, native environments because I tend to keep fish in waters as close to chemically native as possible. And it is not uncommon to see a tank of Amazonians next to a tank of Lake Tanganyikans in my house...

EDIT: Also found an even more specific-to-soft water abstract here:

Aquatic toxicity of magnesium sulfate, and the influence of calcium, in very low ionic concentration water

 

[gerald]

Thanks for that info Jaafaman, and welcome to the forum! I've also read about the importance of natural organic matter (blackwater) for fish osmoregulatoin at low pH and low mineral content. Here's a couple links, and if you search "fish calcium uptake in acid water" or "osmoregulation in soft acid water" you'll find several others. In the 2nd one, artificial blackwater made with commercial humic acid did NOT have the same protective effect against ion loss in soft acid water that natural blackwater did (in Amazon stingrays). Cool stuff.

http://www.lsu.edu/faculty/galvezf/Publications/galvezetal2008b.pdf
http://www.ncbi.nlm.nih.gov/pubmed/12695983

 

[jaafaman]

Would you like to compare Black Water DIY "recipes"?...

 

[gerald]

Sure. My recipe aint too fancy: Mix of rain-barrel water and Raleigh tapwater (tapwater GH and KH each about 25-35 mg/L) and a few handfuls of shed tree leaves (oaks, ash, maple, elm, magnolia). After the alkalinity is used up and pH drops below 5.5, then I add a little aragonite/coral gravel into the filter (~1/2 to 1 teasp for a 10-gal).

According to 2010 Raleigh WTP reports, Ca+ is usually around 6-7 mg/L and Mg+ is around 2 mg/L, pretty close to the "common average" 3:1 ratio (by weight) that you said. For those who like to know molar ratios, that's about 2:1 Ca to Mg, since Ca ions are heavier than Mg. [Ca atomic mass = 40, Mg atomic mass = 24]. I have no clue how much Ca or Mg is in my fishtank water after the original ions are consumed. I guess the aragonite, fishfood, and added tapwater are the only new sources. The conductivity goes up as the tank water gets older, but I'm guessing that's mainly from Na and Cl in the food.

 

[jaafaman]

The Chattanooga area's water runs at about 60 ppm Alkalinity, 70 ppm Hardness and a total of about 120 ppm TDS. Tennessee American Water stopped filling out complete compositions within the WQRs about ten years ago, but a quick e-mail to any of their field crew will net you their Excel worksheet on the samplings.

In addition to the usual Oak leaf and bark infusion (mainly for added color), I use a 35-gallon Rubbermaid trash can with about a gallon's volume of loose, "fluffed-up" peat with constant circulation provided by an open-ended hose powered by a Tetra deep-water air pump. When initially filled, I let it circulate for about a week before I start drawing from it, draining the few gallons I need first through a cheescloth and then through an unbleached coffee filter to remove the larger particulates. The can is then re-topped with fresh tap water.

Every couple of weeks, I turn off the hose and let the peat settle. Then I simply reach into the can and squeeze out a few handfuls of peat to replace with fresh stock. The used peat then gets added to my Earthworm and Redworm cultures running in Rubbermaid tote bins.

The strained water that I've drawn gets a little of the leaf infusion to darken it up just a bit more while adding some of the Oak humics. I then use a Pinpoint conductivity meter to mix in a little RO/filtered water to get the reading I'm looking for before the tank's water change. The conductivity I'm looking for in each case is dependent upon whether it's a breeding or maintenance tank and the species involved. This had been my routine for at least the last decade-and-a-half, and I find the water well-suited for anything from Apistos and Tetras to Altums and Heckels.

Although not nearly as strong as carbonates or phosphates, humics provide a system buffer in their own right, the only requirement being a consistent refreshment. I tend towards small, daily water changes of 15-20% on my soft water tanks, with the occasional double-check on conductivity to keep the tanks fresh and at a consistent environmental level...

 

[dw1305]

Hi all,
Thanks Jaafaman, that is a very interesting post, in a very interesting thread. I've stopped trying to breed "black-water" fish, as this is an area where everything is limestone, and even our rain-water is carbonate buffered. I think I'll give this method a go, and see what figures we end up with.

cheers Darrel

 

[jaafaman]

...I think I'll give this method a go, and see what figures we end up with...

Plan on at least a couple of days' wait for testing runs. Peat's effectiveness in replacing the carbonate anions is almost fully realized after about the first 48 hours of constant exposure, seemingly regardless of the volume tried. You can, in other words, try things out on a much smaller scale such as a five-gallon bucket in order to set a relativistic peat:tap water ratio for the water in your area. When I first came up with the idea while living in Florida, I tested things with just gallon jugs and tablespoons of peat, shaking the jugs by hand at times during the day. I use the large trash can in practice seeking a more stable chemistry across time because of the constant small draws and replenishments, much like a large tank is easier to keep than nano tanks.

Once you've established a base line ratio for your local water and the peat you're using, alkalinity will certainly be less problematic. As far as cutting the cationic concentrations in the post-draw dilution phase, their calculations are at least far more simpler and straight-forward, again making your task the easier. Saves quite a bit in the amount of RO/filtered water required when you let the peat do most of the heavy work from the beginning.

As far as the Oak infusion goes, it's prepared like simple kitchen stock such as chicken or beef broth. Just make sure it's not prepared in a metal container for those unfamiliar. I myself have an old camping cook set with a large, enamel-finished pot that's just about perfect for the purpose. The resulting "tea" is pretty much bacteriostatic because of its chemistry and concentration, so long-term storage in simple, capped bottles isn't usually a problem..

 

[gerald]

1) What's the benefit of cooking leaves+bark, vs just letting it soak at room temp?
2) Regarding TDS/conductivity, does the peat raise or lower it? If so, how? If it's by ion-exchange (divalent ions adsorbed, monovalent released), then I'd expect conductivity would go UP, not down, after a couple days with peat soaking. Am I missing something?

As far as the Oak infusion goes, it's prepared like simple kitchen stock such as chicken or beef broth. Just make sure it's not prepared in a metal container for those unfamiliar. I myself have an old camping cook set with a large, enamel-finished pot that's just about perfect for the purpose. The resulting "tea" is pretty much bacteriostatic because of its chemistry and concentration, so long-term storage in simple, capped bottles isn't usually a problem..

 

[jaafaman]

1) What's the benefit of cooking leaves+bark, vs just letting it soak at room temp?...

A matter of speed and degree. You can, for example, boil water for tea right off, or stick your bags in a jar of water and let the sun brew it.

...2) Regarding TDS/conductivity, does the peat raise or lower it? If so, how? If it's by ion-exchange (divalent ions adsorbed, monovalent released), then I'd expect conductivity would go UP, not down, after a couple days with peat soaking. Am I missing something?

Canadian sphagnum peat has a very high CEC, and it exchanges the monovalent H+ for the divalent Ca+2 and Mg+2. The large influx of hydrogen chews through the carbonate buffers, outgassing CO2 to reduce the alkalinity, remaining to lower the pH. Calcium and magnesium are not only divalent, but metallic as well, normally carrying a higher EC value than hydrogen. Since TDS is a factor of EC (TDS (mg/l) = 0.5 * 1000 x EC (mS/cm)), the TDS would drop through the exchange of cations and the loss of the carbonate/bicarbonate anions.

The amount of humics introduced by the process, particularly tannins, has more of an affect on osmoregulation than EC. Particularly affected are egg membranes, where the introduction of too high a concentration can "tan" the cell membrane and cause reproductive failure when the fry cannot escape its confines as opposed to the egg being destroyed through too high a level of hardness and the egg is in essence "dessicated". It's been my personal experience that a mix of the "doctored" water and enough RO/filtered water to reduce the remaining EC to the TDS conductivity target you're looking for is generally enough to prevent such osmotic damage to even those tissues as sensitive as egg membranes or gill linings...

 

[gerald]

Yup - That's exactly the part I was missing: The exchanged cation (from peat) is H+, which reacts with bicarbonate and carbonate (anions) to make CO2 and water. Electrically conductive ions go bye-bye and conductivity drops. Thanks!

Also that's very interesting about how too much organic matter can inhibit egg hatching and excess hardness causes egg dehydration. I would love to know more about how those phenomena work, if you know or have links to some articles that explain it. The hardness problem is well known of course, but I've never seen a rational explanation of WHY, and the O.M. problem I hadn't heard of at all until now.

Canadian sphagnum peat has a very high CEC, and it exchanges the monovalent H+ for the divalent Ca+2 and Mg+2. The large influx of hydrogen chews through the carbonate buffers, outgassing CO2 to reduce the alkalinity, remaining to lower the pH. Calcium and magnesium are not only divalent, but metallic as well, normally carrying a higher EC value than hydrogen ... the TDS would drop through the exchange of cations and the loss of the carbonate/bicarbonate anions.

The amount of humics introduced by the process, particularly tannins, has more of an affect on osmoregulation than EC. Particularly affected are egg membranes, where the introduction of too high a concentration can "tan" the cell membrane and cause reproductive failure when the fry cannot escape its confines as opposed to the egg being destroyed through too high a level of hardness and the egg is in essence "dessicated". It's been my personal experience that a mix of the "doctored" water and enough RO/filtered water to reduce the remaining EC to the TDS conductivity target you're looking for is generally enough to prevent such osmotic damage to even those tissues as sensitive as egg membranes or gill linings...

 

[jaafaman]

Most of this information has been gleaned over quite a few decades of experience (I'm 56, and started this at 12) as well as participation in the likes of the now-defunct Apisto Mailing List (Hi, Mike!) and the old UseNet News Groups, but a quick stop by Google these days will net passing references to such here and there:

"...Extending the eggs rinsing time to 60 s in 0.10 and 0.15% solutions resulted in a high mortality of embryos during hatching because of hardened egg capsule..."
The effect of tannin concentration and egg unsticking time on the hatching success of tench Tinca tinca (L.) larvae

for something along the lines of toughening the membrane, and

"...Eggs were incubated for 19 h at 26.5°C at six levels of water hardness: 100, 200, 300, 400, 500 and 600 mg/l CaCO3. Water absorption at 100–200 mg/l CaCO3 caused eggs to burst prematurely and minimal water absorption occurred at 600 mg/l CaCO3..."
The effects of water hardness on the hatching and viability of silver carp (Hypophthalmichthys molitrix) eggs

for osmotic transfer. Carp are, of course, a harder water fish than an Apisto, so their roe tend to suffer the opposite effects. Hard water fish roe tend to pass water more easily into the egg while soft water membranes pass water more easily out of the egg, both mechanisms being an evolved trait to cope with the strong osmotic pressure differentials of their environments. Put them in environments of the other extreme and what was an advantage now becomes a distinct disadvantage. Soft water will flood hard water roe to the bursting point because it now cannot pass enough water out of the egg to regain its natural balance. Soft water roe placed in its other extreme cannot take in enough water to cope with its losses to the environment...