Controversy: Dechlor whole tank vs. Dechlor replaced water

[coolchinchilla]

Frequently people advise newbies to treat the whole tank volume with dechlor (prime) instead of just the replaced water when they do a partial water change. Help me understand this concept. It seems counter-intuitive.

Situation:
1. I have a 55 gallon tank with 55 gallons of water in it.
2. That water is totally free of chlorine/chloramine.
3. A week later I remove 20 gallons and put 20 gallons of fresh tap water in.
4. So there are now 20 gallons of new untreated water in and amongst the 35 gallons of treated old tank water. (20 gal new, 35 gal old)
5. Do I put in enough prime to treat 55 gallons of water OR to treat 20 gallons of water?

In my mind, only 20 gallons still has chlorine/chloramines, so I put in enough dechlor for 20 gallons, right? Why treat the full 55 gallons with dechlor when only 20 gallons need to be treated?

Treating the whole 55 gallons would make sense IF you're using prime for MORE than just dechlor -- (i.e., neutralize nitrates.) but for dechlorination only? I don't get it. Is my head dead on this one?

Thanks in advance.

 

[Fishyfanatic]

I treat for the entire tank when using Prime. I believe the bottle states to treat for the entire tank volume when adding tap water that has not been treated, such as with a Python. I would look but I have no clue where the bottle is ATM.

 

[rich311k]

The bottle of Prime does say to treat for whole volume of tank if adding directly to the tank. If you do changes by the bucket you can just dose each bucket.

 

[EdgarMedina1010]

The bottle of Prime does say to treat for whole volume of tank if adding directly to the tank. If you do changes by the bucket you can just dose each bucket.

yep I agree with you

 

[Guest]

The reasons I treat for the entire tank are:

1. You are "mixing" new water with old so doesn't it become one although at a diluted level than just the new. Sure you could dose the bucket but why not make sure? Alot of people also use a Python.

2. 1 capfull treats 50 Gallons so a bottle last a while and it is not expensive to use.

3. It is completely safe to treat for the entire tank and even overdose a little so why not?

 

[src]

Prime treats for Chlorine, Choramine, Ammonia, Nitrites and Nitrates, as well as heavy metals. However, I don't think that the exact dose for Chlorine/Chloramine rich, Ammonia, Nitrite and Nitrate poor tapwater will be as effective if it has to treat Chlorine/Chloramine AND Nitrates.

Think about it - a given amount of prime will only go so far to bind up whatever chemicals are in your water. If the first thing it hits are Nitrates, then it's going to tie up the Nitrates, and leave the Chlorine/Chloramine alone.

So if you treat in a bucket, you can be stingy with the Prime and treat for the volume of fresh water. But if you are adding it to a tank half-full of old water, then there's a decent chance that the "minimal" dose will not do the job you want it to do. It could leave Chlorine and Chloramine in the water. That's a risk that I'm not willing to take. I always dose for the full tank - plus a little for luck.

 

[coolchinchilla]

Ahhhhhh.... the bottle SAYS to treat the whole tank. I get that.

Oh well. I know that prime isn't expensive and there's no harm in putting in extra. I just wanted to know why.

Think about it - a given amount of prime will only go so far to bind up whatever chemicals are in your water. If the first thing it hits are Nitrates, then it's going to tie up the Nitrates, and leave the Chlorine/Chloramine alone.

I thought it was the sodium thiosulfate ingredient of prime that dealt with the chlorine/chloramine. Sodium thiosulfate doesn't have any impact on ammonia, nitrite, nitrate, & heavy metals. So the number of loose chlorine/chloramine ions is the same whether you treat the 20 gallons of new water outside the tank separately OR inside the tank along with 35 gallons of old water. The binding occurs instantly.

I guess I'll just have to accept the notion that the bottle SAYS so and leave it at that.

Thanks for your answers!

 

[7Enigma]

In any tank, and especially a planted tank, there are a LOT of molecules that will compete for Prime and any other dechlor agent that is added. I'd be willing to bet that the recommended dosage of 1ml/10gallons is 2-1 what is actually needed to get rid of the chlorine/chloramines present because of this.

I do PWC's by the bucket and therefore treat the bucket. I eyeball a ml or so (its a 5gallon bucket) and pour it in, then add my ferts and baking soda, then mix with a large glass, and add to the tank. Every 3-4 glasses I mix again just to make sure everything is completely dissolved and distributed evenly.

If I had a larger tank and used a Python, I would most definately dose for the entire tank, and then some!

 

[GodOSoot]

I always double dose just incase for my 40 long...buuut I see that I may just do enough for 75 gals. in the new tank. It could get a little costly otherwise.

 

[ksfishguy]

I treat the entire tank for what it's worth.