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by **Mick e. t.** » 2006-01-19 02:18

Sam is going to hate me for this. For the record osmosis is not the diffusion of one liquid into another. It is the absorption of one liquid into another. To keep this inline with this topic Lets look at what could of been surface's problem with her puffers albeit in another thread. Sudden chemical, toxic or any other shock which is often claimed to be the cause of sudden death in fish, is caused via the process of osmosis. What happens here is for example, a rapid increase in the pH, as the majority of us are aware, will and, can kill fish in the blink of an eyelid. Why? Well the fishes body is in fact a "forward osmosis", (was going to put the obvious but thought better) lol, machine. How it works in a fish is based on a lot of different factors so, in an attempt to keep this just a little shorter I will keep to the bare minimum of details. So a fish is an osmosis machine, what this means is that the water contained within the fish will always be trying to equalize it's self by passing through the body wall ether way. Get this wrong on the out side then because the process is so fast the fish will get it wrong on the inside and, because majority of fish can not control this process it will die from vital organs failing. In very simple terms osmosis is the passing of liquid through a membrane with a view to keeping it's self equal ether way.

RO doesn't even come close to true osmosis. The process here is carried out by filtration, hence RO filter. The water entering a RO filter pass through various stages, all bar one removes different grades of gunge from the water and, unless these function correctly the final phase of this process will fail rapidly. The final phase of this filter is a mesh where the holes are measured in microns or even smaller. It is this mesh which removes or prevents/filters particles as small as ions from passing through it. How it prevents all the hydrogen ions passing through, sorry but, if anyone knows, perhaps they might tell me.
To end, remember that apart from respiration, osmosis is vital to a fishes survival.
One other point, I made reference to a fishes body in terms of a forward osmosis process. This is incorrect as it functions in both directions but, not at the same time,

by **hamburger** » 2006-01-19 08:50

You know Mick your like the wise man guiding us through the dessert. Vielen Dank. :gulp:

by **Surface** » 2006-01-19 13:20

The scarey thing is Ive always topped off my tanks (even knowing that its a nono) but untill sometime last year I used distilled water to do it, then when I looked at how much I paid for all that water as my tank collection grew I changed to tap to top. I am so very thankful for such knowledgable people and for how much I learn everytime I come to this site. No more topping off with tap. :mellow:

by **man-alive** » 2008-11-20 00:44

yes it is a good idea to top off with water that doesn't add to the chemicals and metals in the tank (unless needed) BUT! Water really shouldn't stay in a tank long enough for it to evaporate! Unless of course it is a no filter aquarium.

by **KittyKat** » 2008-11-20 21:17

How do you mean? All of my tanks bar the ones with full lids suffer from evaporation due to the heat from the lights during the day to the point where some of the smaller ones need topping off with 1-2cm of water a day!

by **man-alive** » 2008-11-21 04:32

true true. higher heat with no lids do speed up evaporation. so to be more specific, a medium sized tank with a lid and no excessive heat should do fine until the next water change. of course i am not at your house and can't control the thermostat so this will vary place to place.