copper sulphate as Swimming Pool Algae Remedy?

A. Sounds like you've got a nasty algae there.

First off, I'd reduce pH to 7.2 or 7.1 This will make the copper more soluble and more effective.

Then I'd hit it HARD with chlorine, calcium hypochlorite, until you get up to 4 or 5 ppm which stays up overnight. If you pool is heavily infected, you will likely have to make multiple adds over a few days. If yours is a typical 16' X 32' pool, you might end up using 5-10 pounds or more of hypochlorite. As you kill it off, keep back washing your filter to get rid of the dead stuff.

Consider NOT using CNA. In my opinion it causes more problems than it solves.

You CAN kill it.

Rereading your post - "the previous Chlorine system".

By this do you mean that you entirely stopped the use of chlorine and relied only on copper?

If so, that's wrong. Copper is highly effective against MOST forms of algae, but not all. And copper is ineffective against other possible nasties - bacteria, viruses, odors and others.

Chlorine is absolutely a necessary component. It should be about 1 ppm at all times, with an occasional boost to 2 or 3 ppm.

A. We have an 18' round 54" deep above-ground pool. Every summer we only buy three things …

We already have a small box of copper sulphate we bought at our local tractor stuff store. We mix 1-1/2 cups of the bright blue granules in a 5 gallon bucket of clean water. Stir until all grains are dissolved. We walk the perimeter of the pool in the afternoon and pour all of the mixture in. Then (here's what we buy) we walk around again pouring 5 gallons of HOUSEHOLD bleach ⇦ bleach/sodium hypochlorite in bulk on eBay or Amazon [affil links] . The cheap stuff works for us but don't use laundry bleach. It has less chlorine in it. After adding 2 chlorine tabs (3") to the floaty thing. We wait usually 2 days with the pump on full time. Backwash and rinse our sand filter 2x per day.

By then the water is blue but still can't see the bottom. A trip to the "garden and pool" center at the local WALL place for a bottle of clarifier. This coagulates (clumps together) the now dead algae and brings it to the surface so the filter can more easily filter it out. We walk around the pool pouring straight from the container about half of the thick blue liquid. Again keep the pump constantly running. A day or two later we can usually see the bottom and all the muck. Once we vacuum, this stirs up more stuff (we vacuum while in pool) after that we use the rest of the clarifier in the same manner as before.

Don't get in the pool if the water is green. This could be live algae and getting it in ears, nose or mouth could cause problems. Don't use any more copper sulphate. You can test it if you want but we find our measurement works for us. We only use one dose of copper sulphate upon opening the pool. Only once did we use it twice because we had a very very rainy summer, weren't in the pool often and let the chlorine tabs run out. We haven't had any blond haired beauties turn green on us. We don't use shock either. If you use too much clarifier it could make pool a "white" cloudy. But it will filter in a few days. We are usually vacuuming at 4 days and are swimming about 7 days after starting the routine. We use the recommended dose on the box of copper sulphate for the gallons we have. Use the internet to figure your gallons if you don't know. Have been using this in our above ground with the original liner for 15 years. We do have a sand filter but no ionizer or UV filter or heater. So I don't know if you should use with these. Hope this helps.

A. Jon Stranahan: Your Cyanuric Acid is three times the ideal maximum. It should be 30-50 ppm (the lower, the better, if you can get away with that in Miami). If you are using chlorine, then it isn't doing anything at all at with 150 ppm Cyanuric Acid.

A. Maybe you can use plain copper sulphate, but its solubility is limited. IF you keep your pH on the low side, say 7.1, it may be soluble enough.

Much better to buy chelated copper sulphate based algaecide which is freely soluble. It doesn't need to be expensive since it is essentially permanent, being lost only when you remove water.

A. In fact, copper sulphate is very easily soluble. Prior to dispersing into the pool water it is good to add half of a cooking ladle of CS (ca. 150 gr) into a bucket with water (ca. 10 l), and mix it. Then, taking out continuously the dispersed solution from top and distribute it into pool while filling up more water into bucket and mixing, taking out again, etc., until all the blue powder is dissolved.

A. No worries about Copper Sulphate, the pentahydrate (CuSO4·5H2O), the most commonly encountered salt. Copper (Cu) is allowed e.g. in German standard for drinking water up to 2 ppm. And Cu is contained in CS just by 20 - 25%, i.e., with 8 - 10 ppm CS you get 2 ppm Cu.

During next days the Cu is depleted by reactions with algaes and other unwanted substances in pool water, hence it will be filtered out, backwashed and vacuumed from pool bottom.

And/or farther dissolved by rainwater, by additional water after backwashing, vacuuming.

After CS dissolving it is better to stop the pump and let the CS work. When later added a flocculant (e.g. Alum - a wonderful substance formerly used by our fathers for stopping bleeding after shaving), all will sink to bottom.

BTW, the algaes are not harmful, they just keep the water from being crystal clear, beautiful for our eyes.

A. Hi Jean-Pierre. Garry S claimed that 1 ppm ^ ^copper is quite safe, and estimated that ^ ^{at 0.5 ppm} 100-120 grams ^ ^{copper sulphate} would be required for a 50,000 litre pool (meaning 10-12 grams ^ ^{copper sulphate} for 5000 litres). Jan M says 2 ppm ^ ^copper is safe per German drinking water standards. The USA EPA limit is 1 ppm ^ ^copper. WHO seems to accept 2 ppm but lean towards 1.

This should cover it if you're talking about your own family's drinking water. If you have public responsibility for other people's water I think you need to work on a deeper level with regulatory agencies.

Regards,

Comment:
The 1 or 2 ppm is a limit of Cu for drinking water. Since CopperSulphate contains only 20 - 25% of Cu, the limit for CS can be 4 - 5 ppm (when Cu 1 ppm), event. 8 - 10 ppm (when Cu 2 ppm).

  Thanks, cousin Jan. Garry S suggested 0.5 ppm of copper for algae control and said that it equated to 100-120 g for a 50,000 liter pool and his calculation was correct and based on your copper percentage of 20-25%. For Jean-Pierre's 5,000 liter water tank, that would scale down to 10-12 g, so hopefully we gave him the answer he sought.

But you are correct that my posting was confusing in 2 ways --
-- not making clear which numbers referred to copper and which to copper sulphate (which I have now repaired with superscripts, and
-- reverting to Garry's 0.5 ppm of copper for the calculation while saying 1-2 is probably okay. Thanks for the catch.

Regards,

A. Hi David. You are right about PPM meaning parts per million, but uncertainty is introduced when you ask a 3rd party what someone else meant :-)

Some people might mean parts per million of copper (Cu), others might mean parts per million of copper sulphate (CuSO4), and some might mean parts per million copper sulphate pentahydrate (CuSO4·5H2O = weight of the crystals).

copper sulphate pentahydrate is 25.5% copper by weight, so if you want 1 PPM of copper you need to add 4 PPM of crystals. Good luck.

Regards,

A. Once you are frequently backwashing the filter and vacuuming the bottom (I do it mostly in one go) you have to add fresh water. Consequently, the concentration of the Cu is slowly reduced. And that beside the fact, that the Cu is also diminished by reacting with the algaes. Therefore a timely addition of a new CS portion is needed, especially in the springtime.

As a matter of fact, when e.g. the German standards for drinking water allow 2 ppm of Cu, the 2 ppm in the water for swimming should not make any harm, even if it is a bit over. The 2 ppm does not mean that a tiff or two of it is poisonous, the value is for a precaution if it would be permanently drunk over a longer period of time.

With treating the swimming water by CS we spare ourselves of the daily hassle with keeping a high level of chlorine (to kill the algaes) and also of the difficult (and expensive) job of maintaining of the pH, that is for the chlorine effectivity important but not for the CS.

A. Rassie,
In chemistry, metal ions dissolved into water carry a positive charge, because they are missing electrons compared to their solid metallic state. This means that other ions with negative charges like to stick to them. When this happens, it's called a ligand. The more electrons "missing" from the metal ion, the more ligands can stick to it. Similarly, some negatively charged ions carry multiple negative charges, and some of these are structured in a way that they can sort of wrap around the metal ion and act as several ligands all in one molecule. When this happens, the ions stick together much more strongly than with individual ligands. This is known as chelating, taken from the Greek word for claw, because it sort of looks like a claw gripping the metal ion.

However, I don't know how this specifically applies to a swimming pool. If you're using copper as a disinfectant, I'm guessing you don't want it chelated because that might protect the germs from the copper. "Chelation therapy" is one method used to protect people that have swallowed toxic metals.

A. If the chlorine is granulated then it is obviously organic one with addition of cyanuric acid for stabilizing against UV radiation, prolonging the chlorine effectivity (long term effect). However, the CYA does not evaporate like the chlorine. Once the water is not much replenished, the rising CYA value will reduce the chlorine effect.

Unlike the cheaper inorganic chlorine without the stabilizers, however, without the unwanted problems. As a powder it can be dissolved in a bucket and dispersed into pool water every 4 - 6 days or so.

A. Copper (Cu) allowance for drinking water in majority of countries is 2 ppm (2 mg/liter). If used a copper sulphate(CS - cheap and easily soluble) that contains 20 - 25% Cu, the content of CS can be 8 - 10 ppm, i.e., 10 gr on 1,000 L (1 m3).

A. Your green tinged water may not be an algae problem at all. Next time, try raising the alkalinity aggressively to see if the water turns clear. It might work best if you first lower the ph well below 7 for a day. Be aware of ph of saturation index so you don't go too far out of balance for too long, which will cause other problems.

A. You can simply add water soluble copper salts (i.e., copper sulphate), and ditch the copper anode.

A. Hi Ellori. I appreciate you detailing exactly what your problem is, and providing the size & material of construction of your pool, and I hate to be unhelpful :-(   ... but starting over causes threads to grow to impenetrable length, while launching duplicative ones makes the challenge of finding the answers much harder :-)

So please study the thread and try to challenge an assertion, ask for clarification of something that has been said, or explain what you think is different with your situation. Thanks!

Luck & Regards,

A. Hi Stephen. Others readers seem to have claimed that 0.5 ppm may be enough, but seems very 1-2 ppm safe. 30,000 gallons is about 114,000 liters, so 500 g of copper sulphate pentahydrate would be 0.5/114000 = 4.4 ppm of that material or 1.1 ppm of copper. It sounds like 500 g should be right and 1000 g would be more than needed.

Luck & Regards,

A. Limit of Cu for drinking water is 1 up to 2 ppm (Germany). But when we use the copper sulphate that contains just 20 - 25% of Cu, the ppm can be 8 - 10. And the Cu limit does not mean that it will poison us, it just would not be good for drinking over a longer time period (but we do not drink the pool water, do we? (almost).

There are some measurements for the Cu content (in fact, I have never seen one). I am observing a growth of algae in the gaps between the tiles (in my case). And when there is a lot of rain and/or a lot of new added water after bottom vacuuming and filter backwashing, it needs new dosage. The CS is consumed by the algae marriage, going away with the filtering, backwashing.

It's better to foresee the dosage before the water starts to get greenish, otherwise after the CS addition the water will start to be milky, it will take few days and frequent backwashing to get it clear again. Better to make it in small dosages more often, to avoid a foaming that occur sometimes, also an oily surface can appear - depends on the purity of the CS.

In general, there is no great danger of overdoing as sometimes the pool shops try to scare of the CS. It's much cheaper, much easier and even much healthier than relying on chlorine only and there is no need to care about the pH level (no influence on the CS effect).

A. This is an example of how much copper sulphate to use in a pool and stay below 0.5 PPM.

Taking weight ratio, 1 kg. of CuSO4 releases (63.546 g/mole Cu) / (159.61 g/mole CuSO4) = 0.405 kg. of elemental copper in the pool water. To achieve a target of 0.5 ppm of elemental Cu in 100,000 liters of pool water 0.05 kg. elemental Cu is required.

Therefore, the required dose of CuSO4 is (0.05/0.405) = 0.125 kg. for 100,000 liters of pool water.

I would use this to start with. If there is no effect in a green pool to get it clear within a week I would add a similar dose. You're still at 1 PPM, which is safe for health.

A. I hope that in the meantime your water has cleared up properly. Of course, in the heavy rainy season the water is more prone to algae growth. Firstly, because the heavy rain will bring plenty of dirt and vegetation dust from the air into the pool water. And secondly, the plentiful water addition dilutes the copper sulphate concentration, the algae will be happy for that. Therefore, in that season the CS has to be more often renewed.

The pH value has (almost) no influence on the CS efficiency. It's just good for efficiency of chlorine in case the chlorine also contributes to reduction of algae growth. But with the CS correct dosage it will be managed. Then, the chlorine serves for killing bad bacteria.

Once the CS dosage has not been strong enough and the water has already started getting green the curing will take few more days with an increased filtering and frequent backwashing. That's why it is advisable to keep a proper CS level continuously, the problem will not happen.

A. Hi S. Most readers seem to have suggested that 1-2 parts per million of copper is ideal since it's 'drinking water safe'. copper sulphate pentahydrate (the blue crystals) is 25% copper. So about 4-8 parts by weight of crystals per million parts by weight of water sounds about right.
A cubic meter of water is 100 liters, and a liter of water weighs a kilogram, so about 350 grams.
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey