Why someone should not use chemicals to control the water?

[Drakoi]

Hey there,

I would like to hear your views why someone should not use chemicals to control i.e pH, kH, etc

What do most people do wrong and cause unnecessary deaths to their stock.

We often get "this fish need this parameters" but should we really try to create chemically that conditions?

[Manky Sanke]

Koi ponds are biologically self maintaining ecosystems not chemistry sets. The only chemical addition, if you wish to call it that, is the maintenance of the KH at a realistic level by sodium bicarbonate if the normal water change regime doesn't bring in enough alkalinity. There are other ways to increase KH but since the buffering equation relies on the conversion of bicarbonate to carbonate and vice versa, and filter bugs use considerable amounts of carbonate, I prefer to use exact doses of bicarbonate directly rather than rely on oyster shells etc.

[Duncan]

I must add oyster shell is a pretty poor buffer for alkalinity, the problem is the carbonate is locked into the calcium and the calcium will not release the carbonate till the water turns acidic which in effect kind of melts the calcium so it gives up its carbonate, that's where the term hard and soft water comes from

Bicarb is a much better and instant method of raising KH values

dunc

[Manky Sanke]

Thank you Duncan,

I've been trying to get that message across for ages. The calcium carbonate in shells of all types is insoluble in water above pH 7.0 unless it also has a high level of dissolved carbon dioxide which makes carbonic acid and causes the same effect.

CaCO3 + H2CO3 = Ca++ + 2HCO--
Calcium carbonate + carbonic acid = calcium + bicarbonate

So the only way that oyster shells can add any bicarbonate to water is if it goes acidic or if it isn't properly aerated and has a high level of dissolved carbon dioxide which makes carbonic acid.

[Drakoi]

So, if for example the tab water has pH of 8.0, however I would like to have a pH of 7.0.

Could I let kH reduce, so that pH will start changing, and when pH hits 7.0 because of those swings use bicarbonate to keep it stable?

Could that work ?
Also if not mistaken bicarbonate has a value of pH above 7, wouldnt that affect the current pH in case the above scenario is correct ?

[Duncan]

bicarbonate has a pH value of 8.4 and will raise pH to 8.4 or is capable of lowering pH to 8.4
bicarb acts kind of like a car coil spring if you compress it it rebounds back to its normal length, if you stretch it it rebounds back to its normal length ion the case of bicarb that natural length is 8.4

dunc

[Manky Sanke]

So, if for example the tab water has pH of 8.0, however I would like to have a pH of 7.0.

Could I let kH reduce, so that pH will start changing, and when pH hits 7.0 because of those swings use bicarbonate to keep it stable?

Could that work ?
Also if not mistaken bicarbonate has a value of pH above 7, wouldnt that affect the current pH in case the above scenario is correct ?

It's perfectly possible to run at a pH close to 7 and a KH of about 1 dKH. Many experienced koi keepers do that so as to replicate conditions in Japanese mud ponds BUT...

I never advocate running at such low values unless the hobbyist is fully aware that they are running very close to a pH crash and that maintaining those values requires constantly monitoring water parameters and regularly adding small amounts of sodium bicarbonate, possibly daily. For hobbyists who prefer an easier life, without daily attention to pH and KH, it's far safer to have a KH of around 5 to 6 and to accept whatever pH that causes.

[Drakoi]

Just out of curiousity. gH have nothing to do with the above ? (general hardness) which seem to be infinity Dgh here.

[Manky Sanke]

No, GH is mainly a measure of dissolved calcium and magnesium. It has nothing to do with pH, KH or alkalinity.