Dechlorination and sodium thiosulfate

[Sunny John]

In preparation for draining my pool (new liner on the way) I was looking at threads for dechlorination. I found this thread:
Calculator or instructions for sodium thiosulfate?
and one response referenced another Best Way to reduce Chlorine level. But the latter link appears to be broken? Is there another or a correction? Are these recommendations, to lower FC by 1ppm per 10,000 gallons, still the guidelines?
2.6 ounces weight of sodium thiosulfate
1.5 ounces weight of sodium metabisulfite (some claim up to 3 ounces is needed)
2.4 ounces weight of sodium sulfite
2.6 cups of 3% hydrogen peroxide (2.3 fluid ounces of 27% hydrogen peroxide)

What are the pros and cons for each? Thanks!

 

[JoyfulNoise]

Why do you want to dechlorinate the water? Are you being required to do so by code?

 

[scottts]

Another option is ascorbic acid (i.e. cheap vitamin c powder $20/kg) - 1g lowers FC by 1PPM in 100 gallons of water. So , 100gms to lower 10000 gallon 1PPM. Completely non-toxic.

 

[Sunny John]

Why do you want to dechlorinate the water? Are you being required to do so by code?

It will be drained onto my lawn, and downhill from that is a stream. I don't want to kill the grass, and don't want to put chlorinated water into the stream. I know grass can survive some splashing, but I'm not sure about 22,000 gallons, at around 6ppm, even if i move the hose around and/or stagger the drain over a couple days. I haven't checked local regulations yet...

 

[Darin]

It wont bother your grass and all chlorine will be consumed when it hits the lawn. 6ppm is only double what comes out of the spigot on city water.

 

[JoyfulNoise]

I’d be more worried about the potential impact of the salinity of your pool water (it will be high in sodium and chloride) on the grass. You live in PA so there’s plenty of rain to naturally dilute it but I wouldn’t want to drain during a dry spell or else the brackish pool water will put a lot stress on the landscape.

As for dechlorination, it should deteriorate pretty fast all on its own in a few days. Sodium thiosulfate will add lots of sulfate to the water which may not be healthy for the grass. It really depends of the type of grass.

The impact to the stream will be minimal. 20,000 gallons of water slowly filtering through the soil in hundreds of thousands of gallons of flowing water will have little to no impact on aquatic life. As others have stated, the chlorine residual is going to get used up the second it hits the soil as it will react with all the organics in it.

 

[Sunny John]

Thanks all. The lawn is hardly pristine - there are several types of grass but also clover and more than a few weeds. The lot is over 2 acres and there's no way I'm going to treat that an area that big. I was actually worried more about the water going directly to the stream (which is very narrow - perhaps it should be called a brook? You can jump across it in spots) because it's downhill from the pool to it, but you're right, Matt, most is going into the ground before it gets all the way to the stream. I think I'm just to going to let the FC drift down, not adding any bleach, for a few days before the work starts.

 

[JoyfulNoise]

If you pump out the water slowly, most of it will saturate the ground before getting to the … rivulet ?

 

[Jim365]

It is good you are thinking of the impact chlorinated water may have. I work with large municipal flows and we dechlor the hose streams at the release points. The equipment gets pricey at those volumes.
You have a pool with a pump that probably moves 40 gal/min +/- , totally different quantities.
Matt is correct that slow discharge through the grass will allow the water be absorbed into the ground at those flow rates.
If you want a home version of the dechlor system put the ascorbic acid in a sock or sleeve and place it and your hose end in a large tub/tote. Run the water into the tote and the water will pick up the AA as it is agitated in the tote and then overflows the top to the ground.

 

[Darin]

dont mess with adding anything. The chlorine will be gone when it hits the ground.

 

[techster]

It wont bother your grass and all chlorine will be consumed when it hits the lawn. 6ppm is only double what comes out of the spigot on city water.

Where do you live? I know of no tap water that has 3ppm Cl content.

 

[PoolStored]

Where do you live? I know of no tap water that has 3ppm Cl content.

EPA allows up to 4 ppm chlorine in drinking water. We have had a few members test @4ppm.

At the end user level, you are correct, it is rare to test even at 1/10th that level.

Many water treatment plants add monochloramines instead of chlorine. It is a combination chlorine and ammonia.

 

[Mdragger88]

Where do you live? I know of no tap water that has 3ppm Cl content.

Mine does

 

[Darin]

If you live near a booster station or the plant it will be that high.

 

[JamesW]

For your pool, 46 oz of 3% hydrogen peroxide will lower the FC by 1 ppm.

That is the cleanest way to lower the FC if that is what you want to do.