Backyard Aquaponics
A place to discuss aquaponics

I have been doing some further reading on Aquaponics, courtesy of Slicer.

One item I came across I thought was significant enough to have its own thread, the link is:- http://www.aces.edu/dept/fisheries/educ ... system.pdf

The pages of interest are pages 20 - 23 and discuss water quality/chemistry.

The ammonia table is very handy but the discussion on nitrites explains why aeration should be increased. The recommendation is also for calcium chloride rather than sodium chloride as an additive. I am unsure why this is so and whether it is more effective. I was wondering if anyone had any ideas on this?

Rakocy's chapter on Aquaponics in the Recirculating Aquaculture Systems book says that Na can be toxic to plants and levels in hydroponic nutrient solutions should not exceed 50ppm. Higher Na levels will interfere with uptake of K and Ca.

I believe it is the chloride anion (the cation only effects the chlorides solubility) that combats nitrite absorption in the fishes bloodstream so calcium chloride would appear to be a better option than sodium chloride.

Thanks Alchemist,
Sort of knew about sodium problem with plants but did not realise it was the chloride that combatted nitrite absorbtion.

Just following this through on one of the fish forums it was stated calcium chloride was far more effective than sodium chloride and that potassium chloride was also effective. Both have positives for plants.

Humm... interesting....

Now the question is.... considering we often (as do aquaria and aquaculture practises) utilise salt (NaCl) to combat fungal and bacterial diseases such as "ich"...... is it the Sodium ion that assists in the healing process or the Chloride ion??

Good question Rupert, if we can find the answer to that the plants will be better off
Fish are more suceptible to the fungal/bacterial infections when they are stressed and nitrites certainly do that.

Very good question indeed compelling me to bury my head back in the literature.

A quick google around the traps revealed to me that sodium chloride is a "osmoregulatory enhancer" which in minor quantities helps a freshwater fish balance its natural osmotic processes of losing body salt and taking in freshwater. Osmosis is the movement of water from a region of low salt concentration to one of high salt concentration, across a semi-permeable membrane, in this case the fish's body. (basically to maintain electroneutrality). The addition of salt to the environment will reduce the rate at which the fish takes up freshwater. Sodium chloride seems to be the approved salt for helping this to happen and the most obvious one for fish. However, other salts like calcium chloride can apparently be used.

It seems that external parasitic protozoans have less tolerance to salt additions than fish. Indeed using salt concentrations that fish might like to help balance their system throws parasites into a condition of severe osmoregulatory shock (I guess this means that their freshwater uptake reaches an unacceptable low level)but one mustn't overdo it or the fish might end up in the same condition as the parasite.

good stuff sleepe, keeps the mind working.

people should be aware that calcium chloride will precipitate some carbonates out of the water as solid calcium carbonate

While we are on salt.

I am having to move from my site in Fernhill with excellent water to the north where I think I'll be able to use an alternative site with dodgy water and not that much.

One of its key features is that the water is pretty salty.

Anyway my question is how much salt is going to cause me a problem in my system?

depends what you want to grow. straberries seem very touchy 1ppt bothers them

i think tommies can prolly go 3ppt?

1ppt seems fine for most things.

?

forgive me for asking but my sleep deprived brain isn't capable of doing the conversion from ppt to ppm.

My turn for doing the night feeds tonight

1000ppm = 1ppt

1ppm = .001ppt

Steve and Alchemist

Still persuing this. There are two matters here. One is dealing with cycling and spikes, the nitrite problem. Two is dealing with the fungus etc. Ok there are three not killing or stunting the plants.

For nitrite increased o2 to speed up the conversion of nitrites to nitrates. plus the addition of 'salt' to slow down the effects of nitrites on the fish.

Came across this:-

"There are other chloride ions besides those in NaCl. Calcium chloride has two Cl ions, because calcium itself has two positive charges (Ca++), viz CaCl2. So using calcium chloride for nitrite stress is twice as effective as using salt.

Potassium chloride also provides the same relieve from nitrite, and the K ion can be taken up by plants."

If statement one is correct we should be able to use half the usual dose of 'salt' and hopefully no probs with the plants.

Steve . What is likely to cause the precipitation of solid calcium carbonate and what problems are we likely to have. I would have thought that when the system had cycled and there was a tendancy for ph to drop this would simply buffer the system.

(as an aside it appears supplementing the fish feed with calcium increases or assists with gill function, helps with both nitrite (stress) and ich.)

This is starting to get too long so at this point I would favour a mix of salts higher in calcium chloride, second possibly Potassium chloride with a small addition of sea salt at a level in total below what we would normally use.

Hi Sleepe,
mmmmm Statement one is wrong if they are talking about using the same weights of NaCl and CaCl2. To get to the chloride availability for combat of nitrite one has to consider the atomic weights of the components of the salts. I've done a rough calc. on this (AW Cl =35.5, K, Ca about 40, Na 23) and if you use the same weight of each of the salt the chloride availability is:
CaCl2 64% of the total weight
NaCl 60% of the total weight
KCl 46% of the total weight

This means, as far as nitrite combat, you should get an equal effect from the same weights of CaCl2 and NaCl assuming that all the CaCl2 remains dissolved (and doesn't precipitate out as CaCO3 in alkaline conditions as Steve talks about). KCl has a lesser chloride effect but is readily soluble and won't precipitate.
As far as the plants, K and Ca additions are both beneficial but Na is not, as discussed.
As far as parasite combat, NaCl is the approved salt but other salts such as KCl and CaCl2 should work since you are increasing the salinity of the environment and decreasing the tendency of freshwater leaching into the aquatic organism (see my comment on osmoregulation).

Still working my way through this Alchemist but I follow the 40/23 ratio. If the calcium chloride does precipitate out this leaves the Cl as a gas? or would it more likely combine with something else?
Also I am unsure whether it is atomic weight or ppt that is significant to plants/fish (unless this is the same which I didn't think so)

If the second we could add the same or slightly less weight to achieve nitrite reduction but only increase the ppt by half the amount?

BTW I'm lots worse than Steve at chemistry .