Plop or drop theory makes unfounded assumptions


A few months ago, @minnowette (now apparently one of The Disappeared) said that one of the issues he(?) had with the plop or drop method was that he doubted CO2 diffused out of water rapidly when the shipping bag opened.

This and the assumption that ammonia instantly harms fish are the two weakest assumptions made by advocates of plop or drop.

I thought I'd have to perform my own experiments one day but I still searched for any scientific papers that might shed some light on the subject. It wasn't one that was easy to research.

Last night, I found a paper where they did this:

2020-04-09 01_19_46-Sci-Hub _ A new experimental technique for validating exchange models of c...png

2020-04-09 01_19_16-Sci-Hub _ A new experimental technique for validating exchange models of c...png

You can see that CO2 doesn't dissipate rapidly nor does pH rapidly increase. In fact, it's quite slow.

I previously mentioned that when I supersaturated a tank to 300% oxygen that it took 24 hours to get back down to 200%.

Another study measured CO2 build up in a tanker truck of fish. The tank was open to the atmosphere and the water was agitated by the motion of the truck and a water sprayer. CO2 still accumulated.

Some fish farms use degassing towers to remove CO2. If CO2 in water reaches equilibrium instantly with atmospheric CO2 levels this wouldn't be necessary.

Ocean CO2 levels apparently lags several years behind atmospheric CO2.

I still want to do my own experiments one day but this one's looking busted.

Special thanks to @minnowette for pointing me in the right direction.


I guess here, where bottled water is usually carbonated, nobody even would have thought that CO2 would diffuse from water immediately. That would explain why plop & drop is only a thing here when the fish are obviously already struggling in the bag, but not because of the Ammonia/CO2 reasoning.
Well, learned something today.


Volume of water in the container would make a big difference. I personally have never gotten a bag of fish with two litres of water in it. Reconfigure using perhaps .25-.5 litres, and an open plastic bag rather than a covered beaker. If you're going to conduct an experiment, you should try to match the parameters of the condition you are studying. There are also more variables than discussed in that experiment, variations in temperature being the first that comes to mind. Also there's no mention of ammonia-ammonium in the article.

The other reason for plop and drop is that drip or dip 'n pour acclimation causes the pH to rise regardless of CO2 content, because the acclimation water is going to be at a much higher pH level. I have seen attempted acclimation kill shipments of fish in a store. The CO2 isn't THE factor in the ammonia toxicity, only the pH.


Well, I never used that in defense of using plop and drop, as I only heard that reasoning somewhat recently. I've always plopped and dropped, back when I was just a kid in the late 90s to now, and I never recall killing a fish doing so. There are instances when I would change to drip acclimation, but I never had to yet.


Plop and drop seems counter intuitive based on what we've been taught in the hobby for years but then we used to think an under gravel filter was the way to go.


How can you get 300% o2 Or 200 % for that matter ?
Plop and drop works for me.


How can you get 300% o2 Or 200 % for that matter ?
Plop and drop works for me.

I turn on my oxygen concentrator and 15 minutes later the water is at >300%. It will stay above 100% for over 24 hours.

Similar Aquarium Threads


Random Great Thread!

Latest Aquarium Threads

Top Bottom