Water Changes

[shiromujigirl]

Henry! What a cool backyard scientist you are. Wow, great research.

[HenryC]

SMG, it doesn't take much to spray water into a bucket (although I did place the bucket in front of our orchids so a neighbor would not think I was crazy because I was trying to fill a bucket by misting water at it from 10 feet away). I think you have done far more testing that requires a bit more dedication than spraying a hose for a few minutes.

[Brady Brandwood]

Yes definitely Henry, some great info. *** important*** - glad you're willing to risk your "neighborhood reputation" for the group here.

There are so many myths that neeed to be busted in our hobby.

Best Wishes,
Brady Brandwood

[Bob Hart]

Brandy/Henry/Mike,

In the USA is it really that easy to just 'drill' a well? Althought there is a cost element to doing it, do you not have to 'apply' to abstract the water?

Here in England, water is a commodity which is licenced to abstract it. All new houses and those built up to 10-years or so ago, are also metered, therefore every water change in a pond has a cost elelment to it.

For England, we've had a great Summer. Unfortunatly now, groungwater and raw water reservoirs are low and there has been concern in the South about droughts for next year. Now we've had a lot of rain recenlty, this concern has seemingly gone away, but unless it continues to rain a lot, it may well happen.

[Roddy Conrad]

Henry, the molecular weight of sodium thiosulfate pentahyrate is 248 while the atomic weight of chlorine is 35.5, the molecular weight of Cl2 is 71. If we assume one molecule of sodium thiosulfate pentahydrate neutralizes one molecule of chlorine (Cl2), then the ratio of solid sodium thiosulfate pentahydrate to chlorine would need to be 248/71 or 3.5, not the value given by AES. In fact, the reaction stoichiometry given in the Encylopedia of Chemical technology for the reaction of sodium thiosulfate with chlorine in dilute aqueous solution is:

Na2S2O3 + Cl2 + H2O --> Na2SO4 + S + 2HCl

Like I said above, one molecule of sodium thiosulfate pentahydrate weighing 248 neutralizes one molecule of chlorine which weighs 71.

You may find the remarks I wrote below on an entire pond dying from charging 600 PPM of sodium thiosulfate interesting. The point is that you don't want to use a huge overcharge of sodium thiosulfate because of the possible toxicity of the decomposition products of sodium thiosulfate in a pond environment.

Please note the normal sodium thiosulfate charge is only 3.5 times the chlorine level, so a chlorine level of 3 PPM would need about 10 PPM sodium thiosulfate charge. The ponder discussed below added 600 ppm sodium thiosulfate to his pond, and all the fish died in about 4 days from the sodium thiosulfate decomposition.

Copied/pasted from a post of mine on koivet on this issue is seen below:

The description of sodium thiosulfate pentahydrate in the Aquatic Eco-Systems catalogue states, "Excess levels up to 100 PPM will not harm fish". Well, here we are talking about a charge of 600 PPM which may have slowly harmed fish over a period of several days. So let's think again.

The Acros Chemicals MSDS for sodium thiosulfate states, "This chemical is expected to cause some oxygen depletion in aquatic systems." Well, maybe here is the problem with that huge sodium thiosulfate overcharge? Did the fish run out of oxygen at 600 PPM sodium thiosulfate dose? I don't know....

Now let's see what my old copy of the Encyclopedia of Chemical Technology says about sodium thiosulfate decomposition in a pond environment.....

The stability of sodium thiosulfate solutions are oxygen sensitive, meaning that exposure to oxygen will cause a sodium thiosulfate solution to gradually decompose according to the decomposition reaction in alkaline solution (my normal pond environment):

Na2S2O3 + H2O---> Na2SO4 + H2S

Well, now we have it! An overcharge of sodium thiosulfate can decompose thje thiosulfate to make too much hydrogen sulfide, which will definitely kill the fish. One on line reference says, "Hydrogen sulfide at 0.5 PPM causes hyperpnea, apnea, and respiratory arrest (death) in catfish." We can expect 600 PPM thiosulfate to create 0.5 PPM hydrogen sulfide, it would appear, which will kill the fish. This specific decomposition reaction of sodium thiosulfate is listed as being accelerated by either oxygen contact, or exposue to sunlight. A pond has plenty of both of those!

The decomposition of sodium thiosulfate in neutral or acidic pH is given by:

Na2S2O3 ---> NaSO3 + S

So if the pond water is not alkaline enough to make that very toxic hydrogen sulfide out of sodium thiosulfate, then it will make the less toxic, but toxic nevertheless, sodium sulfite instead. The aquatic LC50 at 96 hours for goldfish for sodium sulfite is 100 PPM, meaning that in 4 days at 100 PPM sulfite concentration 50% of goldfish die.

So if a ponder dumps 600 PPM of sodium thiosulfate in a pond, the fish will die from either the hydrogen sulfide, or the sodium sulfite, concentrations from the gradual decomposition of thiosulfate. And the oxygen concentration may also be depleted, making matters somewhat worse.

I knew there had to be an explanation somewhere in those pages of my chemical books, finally found it.

So the moral of the story is that the overcharge of sodium thiosulfate itself probably did not kill the fish from the sodium thiosulfate concentration itself, instead the decomposition products of that much sodium thiosulfate killed them instead. At least it makes sense to this old chemist.....

[Roddy Conrad]

Here is a list of "simple practical advice" I wrote on the sodium thiosulfate dechlorination in another thread on another board:

Here is my personal advice on using homemade sodium thiosulfate solutions for a dechlor solution:

1. Only mix up what you plan to use in a few weeks since solutions of sodium thiosulfate are unstable, and will decompose when exposed to either air or light. Consider using distilled water to make them up, and consider adding a teaspoon of baking soda per gallon to help stabilize them. Keep the lid on tight, store the sodium thiosulfate solution out of the light somewhere.

2. If you are going to add as much as 1000 gallons of makeup water at a time, consider simply adding a teaspoon of the sodium thiosulfate pentahydrate crystals instead so there is no chance for the sodium thiosulfate to decompose. A teaspoon of the crystals per 1000 gallons is the "right conservative" charge of about 3 PPM for dechlorinating city water.

3. Do not use a gross overcharge. According to the sodium thiosulfate chemical literature, a leading sodium thiosulfate decomposition product at alkaline pH is hydrogen sulfide, which can be toxic to fish at higher doses. So while the sodium thiosulfate itself is not toxic to the fish, its decomposition products in the pond may be toxic at gross overcharges.

4. Do not assume the sodium thiosulfate solution in the pond will be there to dechlorinate the water after 24 hours or so. It will decompose and not be there to guarantee you do not chlorinate the gills of your fish.

5. Avoid using any dechlor of any brand or homemade brew before a PP treatment, since the PP will have to react away all the dechlor before it will do you any good for its intended purpose. In other words, preferably either wait 4 days or so after a water change before any PP treatments, or spend a bunch of PP getting rid of excess dechlor before PP'ing the pond.

I was lots more conservative in both my sodium thiosulfate calculations and doses before I realized that a large sodium thiosulfate overdose can decompose to generate enough hydrogen sulfide to hurt the fish. When I got some recent stories of that actual occurrence, and checked it out in the chemical literature, it made more sense to me to suggest lower sodium thiosulfate doses, but in the solid form so it has no chance to decompose before dechlorinating the water.

[Brady Brandwood]

Hi Bob,

Yes, in my area (North Carolina, USA) a person must apply for a "Well Permit" from the County Health Department - the well location is checked by them to see that it is not placed too close to a property line, too close to a septic system, a house or barn, pond, or too close to any other "contaminating source" - the distances from these vary from 10' for property lines to 100' from septic systems. In rural areas here it really is pretty simple.

In city areas, or suburbs, there will likely be more red tape - as one example, the city where my home is charges for "City Sewer Service" based on the amount of city water the house uses - so if a well were drilled, the city would likely want to meter it to see what they can charge for sewer service - they will assume all of the well water will be flowing though the city sewer system. Most people with ponds, swimming pools, and elaborate sprinkler systems are overcharged since little of the water & sewer they are paying for actually goes into the city sewer system.

Best Wishes,
Brady Brandwood

[HenryC]

OK, I'll use a 3.5 ST to chlorine ratio in the future. So the dosage I normally use will treat 100 gallons of water with 2.9ppm chlorine, not the 3ppm I thought it would (I normally use a little extra anyway).

600ppm ST in a pond! In a 5000 gallon pond that would take over 11kg or 25lbs of ST. That's just a little bit more than the few grams we would normally add during a typical water change.

Thanks Roddy

[Roddy Conrad]

The ponder who killed his fish from the 600 ppm sodium thiosulfate dose dumped an entire 5 pound jar of sodium thiosulfate pentahydrate from AES into a 1000 gallon pond all at once. It took 4 days for all the fish to die. 5 pounds in 1000 gallons calculates to precisely 600 ppm. According to AES literature (which I don't believe), if the ponder had only dumped 1 pound instead of 5 pounds in the 1000 gallons, the fish would have been expected to survive.

[MikeM]

HENRY: About how long was the water sitting before you measured the chlorine level? .... I've just always accepted the statements that chlorine dissipates in a 24 hour period & now I'm doubting that.

RODDY: Great info.

BOB: Well permitting requirements will vary from non-existent some places to virtually impossible elsewhere. Generally in Florida it is not difficult to obtain shallow well permits, but increasingly difficult to get deep well permits allowing water to be drawn fron the Floridan Aquifer.

BRADY: Hope the cold wave doesn't linger too long in NC.