uses of kalkwasser

[hammy]

many reefkeeper have been using kalkwasser to replenish calcium concentration, maintain alkalinity and raising pH. This is common to all.

but is it true that kalkwasser can also precipitate out phosphate ? calcium phosphate as precipitate ??

[blueheaven]

Yes that's true and do you know that kalkwasser actually aids skimming through saponification?

[hammy]

Yes that's true and do you know that kalkwasser actually aids skimming through saponification?

whao .. thanks blueheaven.

saponification is a difficult word for mi.

skimmer work better after dosing kalk.

care to explain... thanks !

[blueheaven]

Basically, it's the hydrolysis of fat molecules by an alkali (in this case, calcium hydroxide) to form soap which the skimmer takes away as the foam collected in the skimmer's cup

[iantoh]

hi there hammy and bh,

i kind of beg to differ with regards to this issue. theoretically, it is possible for kalk to cause the abiotic precipitation of phosphate in the form of calcium phosphate, but i doubt this precipitation will occur in any significant amount. i mean, the chemical reaction for that to occur should also occur with the supplementation of other calcium additives, like near the region where ca reactor effluent enters the tank's water body, so i dont see kalk as a significant aid in reducing phosphate levels, though of course, kalk is better than no supplementation.

by this i dont mean to denigrate kalk or anything, because i use kalk too, and its a great balanced formula, but it has its limitations because it requires dilution, and can only be added as top-up water, and not more, lest it affect salinity negatively.

hammy and bh, just a query to bring up- ive thought about this before but didnt come to any conclusions- say kalk causes the formation of calcium phosphates, and settles on the sandbed. given that bacterial activity often lowers the ph within the sandbed, is it not likely that this calcium phosphate might then be dissolved by the low ph conditions and consequently leeched back or returned to the water column? please correct me if theres some fallacy in my logic, but its an interesting idea to me.

cheers,

ian

[blueheaven]

That's an interesting hypothesis Ian

Although I am not very sure, but I think the bacterial activity in sandbeds are not sufficient to lower pH to the extent of reacting with the calcium phosphate.

It might happen in very small, totally anaerobic areas but as you said, the precipitation is not substantial so given that, the process might be so insignificant, it might be negligible to say that it actually has an impact on our reefs.

[ervine]

WOAH... any one can summarise that??

[May&Bruce]

ervine, I can....it means "we are blur and they are clever"....lol I am still trying to understand why pH drops at night and rises during the day

[blueheaven]

pH drop at night is due to the carbon dioxide produced from the respiration of the organisms in our tanks. The carbon dioxide react with water to form carbonic acid which lowers pH.

It then rises during the day when various photosynthetic organisms photosynthesize and take in the dissloved carbon dioxide in the water. Of course, buffers do play a part too but it'll be difficult to explain.

And back to the topic, I have checked and found that calcium phosphate in weak acids, you'll get dihydrogen phosphate ions H2PO4 instead of phosphate ions. So this means that acidity in sandbeds would not cause phosphate to leech back into the system but instead you'll get dihydrogen phosphate.

However, since the precipitate would most probably settle at the topmost layers of the sand, I doubt it will even react since the pH will drop only in the bottom layers

[May&Bruce]

thanks BH