Test Result Query

[pasenah]

what causes a drop in kh?test results are,
calcium=425ppm
magnesium=1320ppm
ph=8.2 mid morning
kh=6.2dkh
as you can see the other results are fine.all salifert kits.
thanks
ben

[gary smith]

hi there, you need a alk of 9.1 to balance with your calcium i think you need some sodium bicarbonate just add a level teaspoon at a time leave 24 hours then check again some of the more experianced hands might give you the exact amount or you can go to andy hipkiss sight and do the calculation just take it slowly and all will be ok :cheers: gary

[xxmattyxx]

A drop in KH is a drop in carbonate levels in the aquarium effectively.

This is used by various organisms in the tank, most notably corals, particularly SPS, coralline algae, possibly a DSB, and also in the nitrogen cycle to an extent (I think). It can also fall if too much calcium is added too rapidly.

Why do you ask, the level you have isnt dramatically out of order, although it needs some tweaking, it seemed you were asking about why should it fall, it falls because it gets used and therefore needs replenishing, thus we use kalk, supplements and or calcium reactors.

Matt

[pasenah]

thanks for the info gary,ive got kh buffer for the job so ill bring it up to that level.

hi matt,you say use kalk or a calcium reactor but dont they rise the
calcium levels.my calcium level stays pretty constant and doesnt drop with the kh.
thanks
ben

[dod]

I think that photosynthesis could reduce the CO2 level without affecting the calcium level. But this might mean that the alkalinity may vary according to the time of day, which in turn might mean that any individual alkalinity reading may need to be taken with a pinch of salt.

Dod

[xxmattyxx]

Photosynthesis will undoubtedly affect CO2 levels in the tank throughout the 24hr period. Thereby affecting pH levels, lower a.m. at lights on, higher p.m at lights out, once all that photosynthetic oxygen has been produced and expelled the CO2.

This is why its suggested adding kalk (which will raise your pH) is done when the pH is at its lowest, thereby hopefully helping to counteract the pH swing experienced in the tank.

Matt

[kim]

CO2 will affect pH but has zero implications for alkalinity.

kim

[salty54]

Couldn't stabilize mine either. Added a calcium reactor and let everything settle again. Found this did the trick. It runs while the lights are on and switches off at night. I heard that your live rock takes up a lot of calcium as well as any hard corals that are in the tank.

[pasenah]

calcium is not the problem ,but have found out that the water holds a lot more calcium than alk if you know what i mean so the drop in alk is noticed

[dod]

Kim

CO2 will affect pH but has zero implications for alkalinity

Alkalinity is the sum of H2CO3, HCO3 and CO3, which are the dissolved forms of carbon dioxide in water, thus alkalinity and CO2 are linked.

This paper would probably explain it:
http://www.nagt.org/files/nagt/jge/abstrac...n_v50n4p389.pdf (http://www.nagt.org/files/nagt/jge/abstracts/Andersen_v50n4p389.pdf)

Cheers,
Dod ;)

[uda]

Originally posted by dod@Sep 1 2005, 22:57
Kim

CO2 will affect pH but has zero implications for alkalinity

Alkalinity is the sum of H2CO3, HCO3 and CO3, which are the dissolved forms of carbon dioxide in water, thus alkalinity and CO2 are linked.

This paper would probably explain it:
http://www.nagt.org/files/nagt/jge/abstrac...n_v50n4p389.pdf (http://www.nagt.org/files/nagt/jge/abstracts/Andersen_v50n4p389.pdf)

Cheers,
Dod ;)

I think you may have got slightly the wrong end of the stick here. You want to read this Randy Holmes-Farley article (before Kim reads the above ;))

The important bit is here:
"One of these facts is termed The Principle of Conservation of Alkalinity by Pankow ("Aquatic Chemistry Concepts", 1991). He shows mathematically that the total alkalinity of a sample CANNOT be changed by adding or subtracting CO2."

The whole article is here: Alkalinity: Marine Aquarium (http://www.advancedaquarist.com/issues/feb2002/chemistry.htm)

The book he quotes can be had here: It's a bit dull but well worth a read.
Aquatic Chemistry Concepts (http://www.amazon.co.uk/exec/obidos/ASIN/0873711505/interactiveda51-21/026-9370736-7924416)

It is a confusing issue and some of the stuff on the net is very wrong.

HTH

Andrew (UA)

[kim]

Thanks Andrew,

:lol:

Guys, think about it for 5 seconds. If you dissolve CO2 in water:-

CO2 + H20 => H+ + HCO3 -

So one additional bicarbonate ion, one additional hydrogen ion. Buffer increased by one, but at the cost of increasing acidity by one. One adds to alkalinity, one subtracts from it. Net change in alkalinity is therefore zero. I'm sure that RHF in that article will define the alkalinity in terms of a "titration end point". The implication is that alkalinity is not simply the sum of all buffering ions, but the excess of buffering ions to hydrogen ions. So dissolving CO2 doesn't change things.

If you hate chemistry, think as follows.

Alkalinity measures the difficulty of reducing the pH to a set target. This in turn depends on both the buffering capacity (the resistance to change) and also the initial pH (how far do you need to go to reach the target). Dissolving CO2 increases the resistance, but shortens the distance we have to push. Net advantage is zero.

:)

For the same reason, simple photosynthesis won't reduce alkalinity (by consuming CO2) as is sometimes (often) stated.

kim