Optimising Your Aquaponics System

[GaryD]

Hi,

For those who may be interested...........Optimising Your Aquaponics System - Part 1.

Gary

[GaryD]

Hi,

Paul (aka Crusty) posted a comment on my blog in response to Optimising an Aquaponics System - Part 1 and I thought that it was too valuable not to be should be shared with APHQ members.

Well said.

I would go easy on the salt addition, especially if you do not know how much salt is in the system before you treat it (EC/TDS meter anyone?). Sure it provides benefit to the fish but in a well stocked and managed system, you will not really need it as a prolonged exposure. If you do it is best to treat the fish outside the system at a higher dose.

Remember sodium chloride is not taken up by plants to any degree, especially sodium (chloride in small amounts) and therefore accumulate. It is diluted when you top up your system with new water but generally, you will be exchanging, on average 5% of your water per week, which means it can take up to 20 weeks (5 months or longer in winter) to completely dilute the salt.

Sometimes in the back yard, having more tanks for treatment is not often the case, though it is a good idea. Also handing fish is not much fun for both the human and the fish, so permit me to provide you with a solution:

• Lower the water level in your fish tank to half
• Store that water elsewhere for reuse.
• Increase the aeration with adequate air stones.
• Treat the fish at the required salt level for the issue you are having (usually no more than an hour).
• Then fill the fish tank back up again to dilute the salt by 50%. Fish treated, salt use reduced, fish not handled, no spikes in your hands, everyone happy.

Important to note, Aquarium stones are not adequate and if you do not have an air pump, I strongly suggest you invest in one sized for your set up. As the salinity of the water increases, the oxygen saturation of the water lowers so air is really needed.

I might add that any changes or disturbances, cleaning etc.. are best done when the temps are low, like now in Australia. It is good practice to make any big changes to your system when everything is happening a great deal slower (when it is cold). This will get everything sorted, clean and ready for the next growing season.

Keep in mind that for every 5C temperature increase, everything (nitrification, respiration, pooing, metabolism, feeding) increases by around 50%. So while all the organisms in your eco-system are having a rest, it is a great time to get everything nice and ready for the next growth season.

Trying to clean your grow bed in summer may have a negative effect on everything else living in the water with it.

Enjoy!

Thanks Paul........for some very useful tips. Your comments add real value to the blog post.

Gary

[arachdog]

Remember sodium chloride is not taken up by plants to any degree, especially sodium (chloride in small amounts) and therefore accumulate. It is diluted when you top up your system with new water but generally, you will be exchanging, on average 5% of your water per week, which means it can take up to 20 weeks (5 months or longer in winter) to completely dilute the salt.

It'll take a lot longer than that, in fact it will never be 'completely' diluted. You have to remember that each successive water change removes less and less salt. If you start with 2ppt then with a 5% weekly water change, after 20 weeks you still have .75ppt of salt in the system. Even after 40 weeks you still have .27ppt.

[Crusty]

It'll take a lot longer than that, in fact it will never be 'completely' diluted. You have to remember that each successive water change removes less and less salt. If you start with 2ppt then with a 5% weekly water change, after 20 weeks you still have .75ppt of salt in the system. Even after 40 weeks you still have .27ppt.

Good point.

If we are talking about replacing water that has evaporated and transpired not taking any of the water out (with salt in it), the salt will never be diluted at all, ever. In fact it will get stronger. As the water is evaporates/transpires, the salt is left behind, so it gets stronger, then diluting the stronger brings it back to the where it was... On the other hand, if you are removing water by back washing a filter, then arachdogs assessment stands. Some people will be doing both. Even most source waters will contain salt. For example if you are using town water to top up in Australian coastal towns, that water can contain on average 40mg/L salt and inland town water can contain up to 250mg/L. An EC/TDS meter will give you a higher reading due to the nutrient salts that also build up and this will also depend on the solids in your system. As you can see the variables go on and on. My example is just to give you an idea without rambling on about the many variables that effect the salt levels in any system, and caution the use of additional salt ("If you do it is best to treat the fish outside the system at a higher dose").

So Arachdog point, emphases the dangers of additional salt.
.

[GaryD]

Hi,

Of course, the whole dilution question is less of an issue if you are using the water to irrigate soil-based gardens or other growing systems that are not connected to your system.

Gary

[arachdog]

...in fact it will never be 'completely' diluted

Actually not entirely true thinking about it, there would be a finite number of water changes to achieve complete eradication. You wouldn't be able to calculate it exactly, but you could work out the probability that it would be achieved after a certain amount of water changes.

I got bored and had a go:

Nice simple example, 1 ton tank, 2ppt salt.
Weight of dissolves NaCl = 2000g
Tank size = 1000L
No of atoms in a mole =6.023E+23 (Avagadros constant)
Weight of 1 mole of Na=6.941g
Weight of 1 mole of Cl =70.906g
Total weight of 1 mole of NaCL = 77.847g

Total No of moles in tank = 25.69142035
Total number of molecules = 1.54739E+25

Then I whacked that number into a spread sheet and removed 5% of the atoms each time, surprisingly after 1130 iterations there would be less than one atom left. Of course that's not exact because when there's only a few atoms zinging around some of your water changes might not achieve anything at all. But it would be pretty close to that figure, a lot less than I thought to be honest.

Now if that kind of information isn't useful to the average backyard aquaponicist then I don't know what is. LOL.

[GaryD]

Now if that kind of information isn't useful to the average backyard aquaponicist then I don't know what is. LOL.

Yeah.......we should be selling this stuff.

Gary

[arachdog]

On a slightly less esoteric note, has anyone considered using potassium chloride (KCl) instead of regular salt in this application? As I understand it its the chloride ions that have the detoxifying effect on nitrite so I see no reason KCl wouldn't work just as well, and the potassium would be absorbed by the plants far more quickly since its a macro-nutrient. But to be honest I haven't thought it through for very long, there might be a good reason not to do it.

[Crusty]

I think we may be getting off track here....

Actually not entirely true thinking about it, there would be a finite number of water changes to achieve complete eradication.

Then I whacked that number into a spread sheet and removed 5% of the atoms each time, surprisingly after 1130 iterations there would be less than one atom left.

Now if that kind of information isn't useful to the average backyard aquaponicist then I don't know what is. LOL.

lol even I had trouble with that one mate. If you were using demineralized water it would work...

On a slightly less esoteric note, has anyone considered using potassium chloride (KCl) instead of regular salt in this application? As I understand it its the chloride ions that have the detoxifying effect on nitrite so I see no reason KCl wouldn't work just as well, and the potassium would be absorbed by the plants far more quickly since its a macro-nutrient. But to be honest I haven't thought it through for very long, there might be a good reason not to do it.

It is used as a replacement salt (non sodium). I think it definitely has merit Arachy. Not giving it much thought either, but I would be interested to know the potassium:chlorine (chloride) ratio. That would give us the treatment level for nitrite. Anyone have this info? The other thing to watch for is too much chloride, the plants will not like it at all as chloride competes with nitrate uptake from memory... The potassium will be handy within that 7 to 14 days of flowering plants for sure.

Worth more thought.

[arachdog]

but I would be interested to know the potassium:chlorine (chloride) ratio.Anyone have this info?

One to one, KCl Same as NaCl.

I guess it comes down to whether chloride ions are just a big a problem as the sodium ions. If so then substituting with KCl probably isn't going to achieve much.