Backyard Aquaponics
A place to discuss aquaponics

Hi Sleepe,

Here is my explanation but it has involved a few drafts, half an hour or so, and may still not be intelligible :- (

First up carbon dioxide (CO2) dissolves in water to some extent to form carbonic acid (H2CO3). This carbonic acid is a weak acid and therefore only partially dissociates to give limited amounts of hydrogen ions and carbonate ions in the water as follows:
H2CO3 -> 2H(+) + CO3(2-)
Positive ions are called cations and negative ions are called anions... anyhow.....these carbonate ions are present to some extent in the water and if there is a cation around with which they can combine to form an insoluble salt, they will do it and precipitate (drop out) of the solution.
Now CaCO3 has only limited solubility in water so if a calcium cation is present in the water, it will more than likely hook up with a carbonate anion (governed by the solubility of this salt) and become insoluble CaCO3 ...and drop out of the current action. Note that this will leave a hydrogen cation behind but its charge will be quite happily balanced by the chloride anion also left behind.

The chloride, therefore, remains as it is, a (negatively charged) anion in the water). This is important to the extent that the nitrite combat reaction (which needs chloride ion only) won't be impaired by the calcium dropping out. Nor will the parasite combat reaction be impaired because the overall salinity (the total ionic concentration) will remain the same. In theory, the difference is that hydrogen cations have replaced calcium ions which will impair the availability of the Ca ions for the plants....but in practice the use of shell grit or other alkali buffers by fish growers not only neutralises the acid that is generated in this way but in so doing also introduces cations (Eg Ca!!!) back into the system as it dissolves.... a big circle in fact. Ain't nature and chemistry wonderful???!!!

The relevant reactions in the water are : (BTW all the charged ions usually have (aq) = aqueous written after them to denote that they are running around in water.)

(1) the dissolution of the calcium chloride in the first place
CaCl2 -> Ca(2+) + 2Cl(-)
(2) the dissolution of carbon doxide in water and the partial dissociation of carbonic acid
CO2(gas) + H2O partially -> H2CO3 partially -> 2H(+) + CO3(2-)
(3) the precipitation of calcium carbonate from the water solution
Ca(2+)+ CO3(2-) -> CaCO3 (solid)
(4) the neutralisation of the acid generated, by the buffer, which in this buffers case, is just the reverse of the partial (reversible) reactions above
CaCO3 -> Ca(2+) + CO3(2-)
CO3(2-) + 2H+ -> H2CO3

Phew! Incidentally, I reckon Steve knows a fair amount of chemistry aside from other thgings, self-taught or not.

Sorry Sleepe,

Despite the long spiel, I didn't answer your query about AW and ppt. They are very definitely different.
ppt stands for parts per thousand and is a measurement of concentration BY WEIGHT. (eg grams of the stuff per 1000 grams of solution).
Knowing the atomic weights of the components in the stuff actually enables you to work at the level of the chemical reactions and from there to work out what total mass weights of the component you need.
Fish and plants, just like everything else undergo chemical reactions. Once these are understood (which involves working out atomic or molecular weights of the components in the reactions) the weights of comonents needed to do the job become known.
For practical purposes, ppts or ppms (parts per million) of the amount of stuff needed is what we want to know. Then we can just get a weighing balance out and do the business.

Alchemist

This is going to take quite a while to digest. Thanks heaps for the explanations .
I used to do hydro and I have kept fish for a while, putting them together in AP is a whole new ballgame.
What I am trying to get is a workable strategy/theory for when I build a bigger system and it goes into HSM, rather than my usual guess what to do

:blush: thanks AC

and big points for taking the time to post this stuff

this may also be of use to people.

http://www.backyardaquaponics.com/forum ... .php?t=586

not by me, plagiarised

Thanks Steve. I had time on my hands today to devote to the forum but I should have waited for you to dig up the "bible" on this water chemistry stuff. I had to work from first principles and that is hard...but maybe good for me to keep learning and thus combat the ageing process

A couple more interesting links

http://www.aquagreen.com.au/files/Aquag ... rowing.pdf

(contains description if nutrient mix for aquatic plants)

And

http://aquaticconcepts.thekrib.com/

Although these are for planted aquariums, some of it is relevant to AP

Alchemy & Steve,

i have found that working in grams per liter instead of ppt is a lot easier for people to understand and when dealing with water, generally assume 1 for SG and then weight can be used. so 1000ppm=1gram per liter (g/L)

to really explain atomic weights we need to introduce the theory of the mole!!

Fair enough on both counts....but does anybody want to know about moles of the chemical variety or would they rather just stick with weights of stuff required per weight (or volume) of solution??

Your right Alchemist, went too far back into first principles regarding AW

Thank you Alchemist
For your post 23/08 re water you have just awnserd all my question on calcium /sodium /potasium . never crossed my mind to go to atomic weight.

Aquapotter

I just read through the link that was posted at the start of this thread, and I am a little excited. Where I live gets pretty cold in winter and have been wondering how to maintain bed and water temps. So far I have put all beds and fish tank in my shed with lazer light sheeting on the north facing walls.

I have been toying with the idea of using one of those solar pool heaters that cost around $500. This coupled to piping in the growbeds hmmmm....?????
Any thoughts would be well accepted

How would you isolate the flow through the piping/growbeds during summer Bazz.....

Suspect that the heat transfer during summer might raise your water return to the fish tank too high.....

Bazz

Link http://www.builditsolar.com/Experimenta ... htm#Double

Should keep you busy for a while, got heaps of stuff on it.

Certainly wouldn't spend $500

Rup,

Was thinking of a bypass valve to turn it off when not needed, was thinking of 13mm black poly in a U shape under my hydroton

How do you convert an electrical conductivity reading in to a salt content in ppm or ppt?

From my initial reading you can't but can you estimate?