CHEMISTRY
AND THE AQUARIUM by RANDY HOLMES-FARLEY, Ph.D.
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in part by:
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Tap
Water in Reef Aquaria
Many
aquarists ask whether it is acceptable to use tap water
for their reef aquaria. The answer obviously depends on
what is in their tap water. We have all heard of aquarists
who use only tap water and are seemingly very successful.
We've also heard the opposite, such as folks that had significant
problems until they purified their water. How is an aquarist
to decide what to do?
Aside from the
standard concerns about chlorine and
chloramine,1 there are a variety of chemicals
to be concerned with. One source for information on these
chemicals is the annual water quality report from your municipal
water supply, if on a public system. If you have a private
well, you may need to get a test of your own water to know
if it is suitable.
In this article,
I will review some of the chemicals to be concerned with
in tap water, and will show how 18 randomly-chosen public
water supplies stack up. The chemicals to be concerned with
generally fall into two groups. The first group is comprised
of nutrients that may result in ongoing algae problems in
the aquarium. These include phosphate, nitrate, and silica.
The second group
is much broader, and includes those chemicals that are potentially
toxic to reef aquarium inhabitants. Many of these, such
as pesticide residues, are also toxic to humans, so elevated
levels are unlikely to go uncorrected for long periods of
time. Some, however, are more toxic to reef aquarium invertebrates
than to humans. Copper falls into this category, for example.
Consequently, the allowed levels of certain ions in drinking
water can be higher than is acceptable in a reef aquarium.
As will become
clear in this article, using tap water is risky business.
Short of testing your own water, there is no way to be certain
that your water is acceptable. Some testing with kits is
likely desirable, but certain tests will require professional
labs. The data supplied by the water company may tell you
that the do not want to use it, but it cannot guarantee
that yours is acceptable. Consequently, I generally recommend
that folks not use tap water. However, if you choose to
do so for cost or other reasons, I give some recommendations
at the end of the article that are worth considering if
you do use it.
Water Quality
Reports
All public water
supplies in the United States that supply more than 25 residents
are required to supply customers with an
annual water quality report. While there are specified
guidelines on what should be in the report, in practice,
the reports can include a wide variety of different types
of information. Not all reports will cover all of the chemicals
that aquarists are interested in. In fact, of the 18 that
I surveyed, only two said anything about phosphate and only
four said anything about silica. Often, water supplies compile
monthly water quality reports that include much more data
than the yearly report to customers. The October
monthly report for my water supply includes data for
more than 40 different inorganic compounds, even though
only a few make it into the annual report. These monthly
reports are not always available online, however.
Confounding
the interpretation of such reports is the fact that the
potential impurities to be concerned about come from different
sources. Nitrate typically comes from the source water (river,
well, reservoir, etc). Silica and phosphate can come from
the source, but can also be added to the tap water to raise
pH and thereby reduce corrosion. Copper and lead typically
come from customer pipes themselves, although my water company
(MWRA)
recently stated that they may add copper to a reservoir
to reduce algae growth. In water quality reports, you need
to be aware of what is being tested: a reservoir, water
entering the supply pipes, or water leaving customer taps.
Obviously, the last is what you really care about, but typically
only copper and lead are tested this way. Other compounds
are tested elsewhere in the system.
If you don't
have your annual water quality report handy, your best bet
is to check their web site. This list of members of the
Association
of Metropolitan Water Agencies has links to many member
web sites.
General
Attributes of Tap Water
In addition
to the "problem" issues with tap water, there are a variety
of test results that aquarists might find useful if using
tap water for a reef aquarium. Some water reports give data
on calcium,
magnesium,
alkalinity, and pH,
for example. Table 1 shows the results for these parameters
in the 18 water supplies discussed in this article. Some
do not divulge any of this information, and some only provide
it in their monthly water reports. Nevertheless, it is apparent
that these values vary considerably. At the bottom of the
table, the same parameters are shown for saturated limewater
(kalkwasser) for comparative purposes.
While the amount
of calcium
and
alkalinity likely to come from evaporation replacement
using any of these water supplies is not going to meet the
demands
of a typical reef aquarium, it may help. Some of the
water supplies provide what could amount to more than 20%
of the calcium and alkalinity needs for a reef aquarium
with low to moderate demand.
The data for
magnesium
is also interesting, if sparse. The amount of magnesium
added varies considerably even within a given water supply,
from essentially none, to what might represent the daily
demand for magnesium in an average reef aquarium (assuming
magnesium is depleted at a rate about 2% of the calcium
depletion rate).
pH
also varies a lot. The pH of evaporation replacement water
will be largely swamped by the pH of the aquarium, which
is more strongly buffered. Nevertheless, if the pH of the
tap water being used is 9.4, that value will be constantly
tugging the aquarium to higher pH (which is likely beneficial
for many aquarists), while using water with a pH of 6.2
might (or might not) be tugging it downward (depending on
whether there is any real buffering at that pH).
Table
1. pH, calcium, and alkalinity in tap water (NR =
not reported).
Before water
is sent into supply pipes, it is first treated by the water
company. Various treatments are performed to improve the
quality of the water, and one of the most important treatments
is to disinfect the water. Often this disinfection is accomplished
with chlorine or chloramine. Since both chlorine and chloramine
are toxic to many organisms, the residual disinfection chemicals
present when the water arrives at your tap must be removed.
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Chlorine can
often be removed simply by letting the water age appropriately
prior to use. Some aquarists aerate it, and others simply
let it sit for a few days. Chlorine can also be removed
with a variety of different commercial products that react
with chlorine and reduce its toxicity.
Chloramine is not so readily removed by aging, and is
more complicated to remove with commercial dechlorinating
products since one must also remove the ammonia. These issues
have been dealt with in detail in a
previous article.1 The main point here is
that if your water supply uses chloramine, you must be sure
that you are treating the water in an appropriate fashion.
Both chloramine
and chlorine are easily detected by commercial test kits.
Regardless of the method that you use to remove them, testing
to be sure it worked is good practice.
Nutrients
in Tap Water: Nitrate
Aquarists with
algae problems should consider reducing imports and increasing
exports of nutrients such as
nitrate,2phosphate,
3 and silica.
4 One way to reduce imports is to be sure that the
water being used to replace evaporated water or to do water
changes does not contain excessive nutrients. Most water
quality reports have data on nitrate. Sometimes it is confounded
with nitrite data, but rarely is there enough nitrite to
be important.
Table 2 shows
the nitrate levels for the 18 water supplies surveyed. The
nitrate levels range from very low (Boston and Orlando,
with less than 1 ppm nitrate as the maximum level) to very
high (New York City, Orlando, and Miami, with more than
30 ppm nitrate maxima). Some aquaria may be able to process
even the highest levels of nitrate in these tap waters without
difficulty. But if excessive algae growth is a problem,
then nitrate in tap water may be a contributing factor.
Fewer water
supplies provide information on phosphate, at least in their
annual reports (Table 3). Some water supplies, like mine
in Boston, supply such information in their monthly reports.
Not all companies have such monthly reports on line, however.
Some reports quote values for orthophosphate (which includes
H3PO4, H2PO4-,
HPO4--, and PO4---)
as well as total phosphorous (which includes orthophosphate
and a variety of other forms). The latter is probably the
important figure if they are different as it all likely
becomes phosphate in the aquarium. With only a few data
points to interpret, the data look to range from low to
incredibly high at up to 5.4 ppm for New York. Using water
with 5.4 ppm total phosphate would pose a serious risk for
both algae problems, and inhibition of calcification of
corals.
When I first
started a reef aquarium, it was the very high levels of
silica in my tap water that lead me to purchase an reverse
osmosis/deionizing system (RO/DI) to purify it. In retrospect,
that reason may have been faulty, as I now add
silica4 to my aquarium in about the same
amount as if I were using tap water to replace evaporated
water. Nevertheless, I am also glad that I use RO/DI purification
for the concerns about metals that are discussed later in
this article.
However, many
aquaria, especially new aquaria, can suffer from problems
with diatoms. In such a system, silica in tap water can
significantly contribute to the problem, with tap water
having as much as 80 ppm silica in it (in Albuquerque; Table
4). At that level, even mature aquaria may have significant
difficulties dealing with the silica additions from evaporation
replacement and water changes.
One of the biggest
concerns for aquarists considering the use of tap water
is copper. Copper is more toxic to marine invertebrates
than it is to humans, so the EPA allows more in tap water
than an aquarist would want in an aquarium. Specifically,
the EPA has an action level at 1.3 ppm copper in tap water,
and it is only a big problem (to the EPA) if more than 10%
of the homes on the water supply exceed that level. For
that reason, water supplies typically report the 90% level,
meaning that 10% of homes exceed that stated value. Many
also report the maximum level in any home tested.
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Table 5 shows
copper levels for a small selection of homes for all of
the cities in this study. The reason that copper must be
tested at the home tap is that most of the copper in public
water supplies comes from the pipes in the home itself.
Further, newer does not necessarily mean better, as fresh
copper pipes might be even more inclined to release copper
to the water than those that have had decades to build up
protective coatings.
How much copper
is too much? That is difficult to say, and certainly varies
from organism to organism. In a
recent test,5 Ron Shimek added copper to
natural seawater and looked at the effect on sea urchin
larvae. He found that concentrations above 10 ppb decreased
the larval survival after 48 h, and that concentrations
above 100 ppb killed all of them. Whether that translates
into particular copper levels to be concerned about in typical
reef aquaria is open to discussion. Nevertheless, it points
out that copper is potentially toxic at levels well below
the EPA action level of 1.3 ppm. That hypothesis is well
supported by the
literature on copper toxicity.6
Canadian Water Quality Guidelines for the Protection of
Aquatic Life suggest that copper be kept to less than
a few ppb in fresh water, but they do not provide a salt
water recommendation.
So how do the
water supplies stack up with respect to copper? For some
homes, not well. Ten percent of the homes tested in Miami
have more than 1100 ppb copper in their water. In Kansas
City, Orlando, Phoenix, and certain districts in Houston,
ten percent of the homes have more than 500 ppb copper.
At least one of my neighbors in Boston has 1100 ppb copper.
What's the best
case? That's hard to say for sure, but perhaps Central Arkansas,
where ninety percent of homes have copper below 50 ppb.
Nevertheless, ten percent of homes are above that level,
and some may be significantly above that level.
Based on the
data, if your home is among the highest in your district,
your water likely will be unacceptable. Since most aquarists
do not know the copper levels in their water, it can be
a risk to use it. If you do choose to use it, there are
some simple actions that you can take to help:
1. Test the
water for copper with a test kit. Some of the kits available
to hobbyists (
Seachem and Hach
LP Cube, #21938-00), for example) claim to detect copper
at fairly low levels (10 ppb for Seachem and 50 ppb for
Hach). Whether those limits are attained in practice or
not, I do not know. But they likely will easily detect the
very high levels in some tap water (500-1000+ ppb copper).
Thus they can at least be used to screen out the worst offenders.
2. Let the water
run for 5-10 minutes before collecting it. This will greatly
reduce the likelihood of getting a high copper (or lead)
level from water that has been sitting in your pipes for
an extended period of time.
Water supplies
are also required to measure lead levels. Since lead has
become a significant concern with respect to development
of children exposed to it, the levels of lead in water supplies
have been greatly reduced in recent years. Still, some homes
and water supplies have lead pipes and solder, and those
concerns have been the source of many new regulations by
the EPA (including raising the pH of tap water to reduce
corrosion).
Table 6 shows
data for lead tested at a small sample of homes in each
district. The values obviously vary greatly, from less than
1 ppb maximum in Albuquerque to more than 50 ppb maximum
in Boston and San Francisco.
Whether these
lead levels are a concern or not isn't entirely clear.
There are undesirable effects noted to organisms6
in the tens of ppb lead.
Canadian Water Quality Guidelines for the Protection of
Aquatic Life suggest that lead be kept to less than
a few ppb in fresh water, but they do not provide a salt
water recommendation. It also bioaccumulates in organisms,
so constant low doses can build up a significant body burden.
However, the exact effects in aquaria are not known.
Based on data
such as that shown above, there are many reasons to be concerned
about tap water for use in reef aquaria. In some cases,
especially the nutrients, one can learn quite a bit about
the suitability of your tap water from a water quality report.
Unfortunately, some of the potential problems with tap water
may come from your own pipes, and so may not be reflected
in the report. My recommendation is to be on the safe side
and purify the tap water (via reverse osmosis, deionizing
resins, or any of a variety of other related methods).
If you decide
to use tap water because of the cost of purification, here
are some recommendations:
1. Be sure to
deal appropriately with chlorine or chloramine in the water.
2. Let the water
run for 5-10 minutes before collecting it. This will greatly
reduce the likelihood of getting a high copper or lead level
from water that has been sitting in your pipes for an extended
period of time.
3. You should
consider getting a copper test kit to reduce the concern
that your tap water has very high levels of copper. Seachem
and Hach claim fairly low detection limits for copper. They
likely won't distinguish the lowest levels, or guarantee
that it is low enough to be ideal, but they should highlight
the exceedingly high levels that some homeowners have.
4. If you have
an algae problem, test the tap water for nitrate, phosphate,
and silicate (the latter in the case of diatoms).
