Tropical Fish Forum
Tropical Fish Keeping Help and Advice => New Fishkeepers => Topic started by: pollydoodle on June 27, 2018, 04:57:55 PM
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I have always been one of those people who ask questions. I was a 'why??' child ::) :vcross:
For those who have been following my progress with my new tank, hopefully tonight all readings will be well and I can buy fish tomorrow.
My 'why' question is, if all the readings are ok with the water as it is, why do I need to do a big water change. I'm not doubting the instructions, just want to know the reasoning behind it.
Thank you so much for your patience xx
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It is simply because all the ammonia you have added during cycling is turned into nitrite then nitrate. The big water change is to remove all that nitrate and get the level down to as close as possible to the tap water nitrate level.
It used to be thought that nitrate in the hundreds would not harm fish but it has been shown in the last couple of years that nitrate above 20 does have an effect. So the lower you can get nitrate before the first fish go in the the tank, the better.
Of course some of us have tap water nitrate well above 20 - UK legislation allows up to 50 ppm in drinking water - so water changes won't get it lower than whatever comes out of the tap.
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I would also echo that question and believe that many folks do it simply because "we're supposed to"
Edit: I mean in general terms, rather than ammonia cycling...
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In general terms, rather than ammonia cycling - water changes remove the nitrate made from the ammonia excreted by fish, though if there are lots of live plants there won't be that much since plants use the ammonia. But fish excrete other things as well, things we can't test for. Once upon a time I worked in a hospital chemical pathology lab, and we tested human urine for all sorts of things. Fish secrete similar, if not the same, things which build up in the water. Fish communicate by chemical signals - pheromones are for communication within a given species; allomones are for communication with other species. When levels of these build up in the water they cause stress for the fish, and we all know that stressed fish get sick more easily.
In the wild, rivers and lakes have constant water changes as the water flows down rivers, and into and out of lakes. The chemicals excreted by the fish are constantly washed away. Water changes in fish tanks are the next best thing.
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Just to see, I tested tap water for nitrate 2.5 tank 20
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Your tap nitrate is very good news :) You'll be able to keep the tank nitrate well below 20 ppm when there are fish in the tank.
And with reference to your other thread, since you are not quite cycled yet you'll be adding more ammonia which will make even more nitrate. 1 ppm ammonia is turned into 2.7 ppm nitrite and on to 3.6 ppm nitrate.
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To play Devil's Advocate:
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1 ppm ammonia is turned into 2.7 ppm nitrite and on to 3.6 ppm nitrate.
Sue, can you please provide me with a link to that equation. I know it's correct, but I've looked for it a few times lately to support what I've said in various places and simply cannot find it.
Fish also produce pheromones (allomones?) that inhibit the growth of others of their own species, and often also closely related species. These are also removed by water changes.
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@Hampalong - it's just simple chemistry and arithmetic.
N = 14
H = 1
O = 16
NH3 is 17 (14 + 1 + 1 + 1)
NO2 is 46 (14 + 16 + 16)
NO3 is 62 (14 + 16 + 16 + 16)
17 g ammonia is turned into 46 g nitrite and 62 g nitrate.
1 g ammonia is turned into 2.7 g nitrite (46/17) and 3.64 g nitrate (62/17)
Ppm is x g of something dissolved in 1 million g water so that also means 1 ppm, 2.7 ppm and 3.6 ppm
Those growth inhibiting pheromones are one reason why breeders do lots of water changes on fry tanks.
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@Hampalong - it's just simple chemistry and arithmetic.
Unfortunately Sue, the words "chemistry" and "simple" do not go together.
But that is a remarkably simple explanation. Maybe my old chemistry teachers just couldn't explain it very well. Education back then was more about learning than understanding.
:)
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To me, chemistry is simple but I do have a degree in chemistry ;D But I do realise that just because I find something simple it doesn't mean that everyone else should also find it simple which is why my explanations tend to assume the reader has only basic chemistry, if that. You'll notice I avoided using the words 'atomic weight' etc ;)
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When I did physics A Level, I couldn't get my head around e=mc2 it's just not immaginable. Break something and energy comes out. That like bitinf a pieve of toast and there being an explosion. If I can't see it I don't understand it (because I'm weird like that!). Chemistry therefore is not my topic of choice!
Totally get what Humpalong means by learning not understanding. I just learnt the formula and did my test... never understood it. Neither did I get a good Mark, not like the topics I did properly understand :)
I'm a geographer. Rivers, mountains etc... things you can see! :raspberries
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Although my background is scientific, I could never get a grip of pure chemistry. ???
Biology and biochemistry I get, because I can relate it to real life. Pure chemistry and physics are completely out of my comprehension and leave me feeling utterly bewildered. :blank:
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Engineers, we have only just grasped the need to wash hands going into the toilets as well as on the way out :) Happly use you scientist's ideas though
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I think I am the only chemistry graduate who does not have even an O level in physics, all because the school I went to made us choose between languages and sciences at the end of the 2nd year (year 8 ). I chose languages, dropped physics, then changed my mind a year later when it was too late to choose physics for O level. So I agree totally with those who find physics beyond comprehension ;D
I do have O level maths (I got grade 1 which was the top grade back then) which is why I find it easy to do the arithmetic in post #8, but I couldn't study both maths and biology at A level as the lessons were held at the same time (I did biology), so I find concepts like calculus beyond me.
But I always found chemistry, particularly organic chemistry, to be fascinating.
And I did study A level geography because of lack of other options. Somehow it was my best result ???