Pond Boss Forums GENERAL QUESTIONS Water chemistry Really high alkalinity

New member here - first post. I've been looking around for a bit. Great forum, and just got my first magazine. We just purchased a property with a 6.8 acre limestone quarry pond from the '60s. Our first water quality results from the lab has alkalinity at 919 mg/l CaCO3! pH is a bit high but reasonable at 7.9, and hardness high at 241 mg/L. Any thoughts on what we have? Thanks!

About the best pond conditions anyone could have. The high alkalinity of calcum carbonate is great. What it will do is buffer the water to keep the PH at 7.5-8.5 no mater what you do to it untill you were to raise the acids to above 1000mg/l or even more.

I really hope I can keep my pond there. It is now but I do not know for how long.

Cheers Don.

Hobbyman welcome to Pond Boss.

Do a little looking about the Fla phosphate pits. Phosphate (fertilizer) is mined and because much of Fla sits on limestone the water runs through the limestone into the phosphate lakes . The result is some of the most productive water on the planet. Rates of sustained fish in the 2000-3000 lbs per acre are common. A normal good lake can carry 400 lbs per acre.

That should give you some idea of what can happen with good alkalinity and fertilizer be it natural (yours) or added. Water + limestone/lime + fertile lands (phosphate pit or added fertilizer)= high productivity.

I wonder if Bruce Condello might have something to say about what you can do with a quarry pond...

Thanks a lot for the feedback. Sounds like it's not a problem and maybe good. I was concerned as most of the "good" ranges I was seeing online were something like 20-200 mg/l. Lot's to learn about this pond stuff, but it's going to be fun I think.

Hoo ya if you were to fertilize your pond with good calcium carbonate buffer the results can be staggering.

Very envious of your pond. Wish mine was as big... ho hum..

No saying it's an error but I've never seen that large of a discrepancy between alkalinity and hardness. They usually go hand in hand.

I wonder about the accuracy of the test also. I ran a self-test with a pool test kit previously and thought it was closer to 100 mg/l. Just figured the lab result would be the correct one. I'll have to get another one or two done to really know for sure.

I had a lab test done where I sent off the sample. They said iron was only 0.5 mg/l. I wish! More like 2.5 mg/l. Turns out iron needs to be sampled on site to be accurate. Not sure why they even bothered.

Up here we see this in soil tests in Ontario all the time. We have allot of calcium carbonate in our soils. Its a real funny one in chemistry where it will bring the PH down and PH up. This is why the alkalinity is high (lots soluble) and the hardness is not that high because of the buffer that is soluble. ITs really the test that is flawed then testing for alkalinity. You would expect with high alkalinity that you should have a much higher PH but you would if you didn't have calcium carbonate as your alkaline product that is soluble.

What this will do is if you add fertilizer to the pond it will still be soluble but not have a huge swing on your PH. When it dose go it will go fast but for the size of the BOW it would take tones and tones of fertilizer to do this.

Cheers Don.

Thanks Don. We're going to wait a season to see what's up before we fertilize. All we know at this point is we have lots of mussels, some weeds (chara I think), and at least one ~12" LMB.

Alkalinity and hardness can be different - they are not the same. I will post info below.

SARC

Hardness
Water hardness is important to
fish culture and is a commonly reported
aspect of water quality. It
is a measure of the quantity of divalent
ions (for this discussion,
salts with two positive charges)
such as calcium, magnesium
and/or iron in water. Hardness
can be a mixture of divalent salts;
however, calcium and magnesium
are the most common sources of
water hardness.
Hardness is traditionally measured
by chemical titration. The
hardness of a water sample is reported
in milligrams per liter as
calcium carbonate (mg/L CaCO3).
Calcium carbonate hardness is a
general term that indicates the
total quantity of divalent salts present
and does not specifically identify
whether calcium, magnesium and/or some other divalent salt is
causing water hardness.
Hardness is commonly confused
with alkalinity (the total concentration
of base). The confusion relates
to the term used to report
both measures, mg/L CaCO3. If
limestone is responsible for both
hardness and alkalinity, the concentrations
will be similar if not
identical. However, where sodium
bicarbonate (NaHCO3) is responsible
for alkalinity it is possible
to have low hardness and high
alkalinity. Acidic, ground or well
water can have low or high hardness
and has little or no alkalinity.
Calcium and magnesium are essential
in the biological processes
of fish (bone and scale formation,
blood clotting and other metabolic
reactions). Fish can absorb calcium
and magnesium directly
from the water or from food.
However, calcium is the most important
environmental, divalent
salt in fish culture water. The presence
of free (ionic), calcium in culture
water helps reduce the loss of
other salts (e.g., sodium and potassium)
from fish body fluids (i.e.,
blood). Sodium and potassium
are the most important salts in fish
blood and are critical for normal
heart, nerve and muscle function.
Research has shown that environmental
calcium is also required to
re-absorb these lost salts. In low
calcium water, fish can lose (leak)
substantial quantities of sodium
and potassium into the water.
Body energy is used to re-absorb
the lost salts. For some species
(e.g., red drum and striped bass),
relatively high concentrations of
calcium hardness are required for
survival.
A recommended range for free calcium
in culture waters is 25 to 100
mg/L (63 to 250 mg/L CaCO3
hardness). Channel catfish can tolerate
low calcium concentrations
as long as their feed contains a
minimum level of mineral calcium
but may grow slowly under these
conditions. Similarly, rainbow
trout can tolerate waters with free
calcium concentrations as low as
10 mg/L if pH is above 6.5. If
freshwater culture of striped bass,
red drum or crawfish is being considered,
free calcium concentrations
in the 40 to 100 mg/L range
(100 to 250 mg/L as CaCO3 hardness)
are desirable; a value of 100
mg/L (250 mg/ L calcium hardness)
matches the calcium concentration
of fish blood. Tests specific
for calcium hardness should be
performed on samples of the
water source being considered for
these animals.
A low CaCO3 hardness value is a
reliable indication that the calcium
concentration is low. However,
high hardness does not necessarily
reflect a high calcium concentration.
But, since limestone is common
in the soil and bedrock of the
southern United States, it would
be reasonably safe to assume that
high hardness measurements reflect
high calcium levels.
A CaCO3 hardness value of 100
mg/L represents a free calcium
concentration of 40 mg/L (divide
CaCO3 value by 2.5) if hardness is
caused by the presence of calcium
only. Similarly, a CaCO3 value of
100 mg/L represents a free magnesium
value of 24 mg/L (divide
CaCO3 value by 4.12) if hardness
is caused by magnesium only.
These factors (2.5 and 4.12) are related
to the molecular weight of
CaCO3 and the difference in
weights between calcium and magnesium
atoms. Where hardness is
caused by limestone, the CaCO3
value usually reflects a mixture of
free calcium and magnesium with
calcium being the predominant divalent
salt.
Agricultural limestone can be used
to increase calcium concentrations
(and carbonate-bicarbonate alkalinity)
in areas with acid waters or
soils. However, at a pH of 8.3 or
greater, agricultural limestone will
not dissolve. Agricultural gypsum
(calcium sulfate) or food grade calcium
chloride could be used to
raise calcium levels in soft, alkaline
waters. Expense might be prohibitive
if large volumes of water
need treatment. Identifying a suitable
water source may be more
practical.
Effects of pH, alkalinity
and hardness on ammonia
and metal toxicities
Ammonia becomes more toxic as
pH increases. Higher concentrations
of the toxic form of ammonia
(NH3) are formed in basic waters;
while the less toxic form, ammonium
(NH4
+), is more prevalent in
acidic waters. Since alkalinity increases
pH, ammonia will be more
toxic in waters with high total alkalinity.
Hardness is not typically
associated with ammonia toxicity.
Metals such as copper and zinc are
commonly used around aquatic
environments (tanks, plumbing
and copper sulfate). These metals
become more soluble in acidic environments.
The soluble or free
ionic forms of these metals are
toxic to fish. High total alkalinity
increases pH and available bases
which produce less toxic or insoluble
forms of copper and zinc.
High concentrations of calcium
and magnesium (hardness) block
the effects of copper and zinc at
their sites of toxic action. Therefore,
copper and zinc are more
toxic to fish in soft, acidic waters
with low total alkalinity.
Ideally, an aquaculture pond
should have a pH between 6.5 and
9 as well as moderate to high total
alkalinity (75 to 200, but not less
than 20 mg/L) and a calcium hardness
of 100 to 250 mg/L CaCO3.
Many of the principles of chemistry
are abstract (e.g., carbonate-bicarbonate
buffering) and difficult
to grasp. However, a fundamental
understanding of the concepts and
chemistry underlying the interactions
of pH, CO2, alkalinity and
hardness is necessary for effective
and profitable pond management.
There is no way to avoid it; water
quality is water chemistry.

Read the fertilizer thread from the archive before any thought of adding fertilizer - you may not need any.

http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=96127#Post96127

That's a lot of info. I'm going to get another alkalinity test done. It sounds like high levels are not necessary but better than low. Same for hardness. Anything I should look at when we thaw out? Thanks again.

I read the fertilizer thread. I'm not fertilizing for this season at least and maybe never. Pond is groundwater with unknown turnover rate (how to tell?), and has plant growth on bottom (chara?). Water is very clear but I first saw it in November so it might green up in summer.

The other thing I would do before stocking is sample the current population of fish. I don't know if an electro fishing survey is in your budget or even if it would be effective on a BOW like yours -- this is a question for a real expert.

If that's not feasible, sample with rod and reel, Fyke net, cast net, or minnow trap and see what you get. Record the species, weight AND length of every fish you land and this will tell you quite a bit about the health of your fishery.

This is what I did and with the help of the PB forum, and using selective harvest I doubled the average RW of the LMB in my pond.

Bocomo, I do have a couple of cast nets and minnow traps. So maybe try some fishing and nets / traps. Weight and measure and take notes. Is there a reference book or something I should get to compare my results to? I understand some of the concepts with bass heavy versus bluegill heavy, but I would have no idea what I was looking at with a bunch of numbers. I just hope we don't have too many unwanted species, but not much to do about it now. Thanks

There are charts for several species in the archives. Look for anything discussing "relative weight" or "weight ratio."

If I were you, I would try to strike up a conversation with Bruce Condello. He has a pit pond and he grows amazing fish.

I did a quick search - lots of charts / references to charts. I suspect we would also want to see fish of each species with some spread of sizes / ages, rather than all big or all small, etc. This is going to be interesting.

Bocomo, I just looked at the link to your old pond project. That's an impressive improvement in the fish quality in one year!