Water conditioner and Fertilizer dosage question

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Fish Crazy
Feb 2, 2007
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Just a quick question on dosing water conditioner (API) and fertilizer (flourish comprehensive)

Say my 75 gallon is full of water and it is time to change the water. I drain 50% of the water and refill. Do I dose water conditioner and fertilizer for the full tank again or do I work out the math and dose for about 35 gallons?

Also API’s water conditioner says dose 1ml for 15 gallons of water to remove Chlorine and add 3ml for every 15 gallons to remove Chloramines.

How much water conditioner am I actually putting in per 15 gallons?

I'm almost afraid to enter this thread on this topic--again. But I will, as I have Neale Monks advice backing me up and truth is truth no matter what anyone believes.

Conditioner is only needed for the volume of fresh water being added. If you want to buy more conditioner to use more, do it if it makes you happy. But it is not necessary, fact. I would, as Neale said, err on the side of caution with a tad more rather than a tad less, as measuring water volume is not always easy. But bottom line is, there is no benefit if you are changing 25 gallons of a 60g tank to dose for 60 gallons, just 25 gallons is adequate. If you use a quality conditioner.

Interesting we now have a third set of numbers for the API... ? First it was 1 ml for 20 gallons, then a bit more for chloramine (understandable), now its 1 ml for 15 gallons. For the record, powerdyne lives close to me so I know our water very well indeed, and there is chlorine (not that much any more) but nothing else. They rely more on UV than chemicals ("yay" shout my fishies!). there isn't much of anything in our water except organics, fortunately.
Here is a pic of my bottle. Would be very odd if different bottles say different things


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Here is a pic of my bottle. Would be very odd if different bottles say different things

That is definitely new. My bottle said 1 ml per 20 gallons, as was shown in another thread today. This for chlorine. Interesting.
I agree with Byron as to there being no advantage to adding more conditioner than actually needed. In my case with a small 20 gallon I treat the new water before adding to the tank and only add as much treatment as needed for what I'm adding.
If you add an aquarium plant fertiliser once a week, and you have a reasonable number of healthy growing plants in the tank, then do a big water change each week and re-dose the fertiliser for the entire tank.
I think it depends on the size of the bottle.

I have two bottles in my cupboard -
The 1 fl oz/30 ml bottle says 1.25 ml per 20 gallons for chlorine, which is the same as 1 ml per 16 gallons. And 1 drop per gallon/3.8 litres water.

The 4 fl oz/118 ml bottle says 1 ml per 15 gallons for chlorine. It doesn't give the dose rate for drops.
(Before anyone asks, the smaller bottle has a dropper lid, the 4 fl oz bottle has a cup lid. As I need to measure drops, I use the 4 fl oz bottle to refill the 1 fl oz bottle)

Powerdyne's photo for 32 fl oz/946 ml says 1 ml per 15 gallons for chlorine.

But.... a few years ago I bought a large 16 fl oz/473 ml bottle. The dose rate for that was 1 ml per 20 gallons. I had to do a complicated calculation to work out how many litres were treated by 1 drop.

@Byron Which size bottle did you have which said 1 ml per 20 gallons?
@Byron Which size bottle did you have which said 1 ml per 20 gallons?

I had the largest size, 2 gallons, and I cannot remember but somewhere I read 1 ml per 20 gallons. I just checked the API site and it says the same, 1 ml for 20 gallons. But if you enlarge the 1 gallon jug photo it says 1 ml for 15 gallons; this is the one powerdyne shows in his photo I've no idea why they have it different, the product is presumably the same product in any size container.


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