Aquaponic Gardening

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For some time now I have been adding salt to our system for the health of the catfish. As a result, the catfish are doing fine. They no longer have skin conditions. I add 10 lbs. of salt to our 1200 gallon system bi-weekly. (The salt has NO additives.)

The plants, on the other hand, have not been doing so well. Most of what we have planted into the system has not fared so well. Swiss chard, for instance, does great. We have been scratching our heads trying to find the problem. The pH runs between 6.2 and 6.6. The ammonia, nitrites and nitrates are also at good levels. My wife was reviewing Sylvia's "rules of thumb" this morning and found some warning about sodium use being non-productive for the plants.

Your educated opinions, please!   If you don't have catfish in your system, you probably don't understand the need for the salt.

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Replies to This Discussion

What Kind of catfish?

I grow channel catfish and they may do well with a small amount of salt but I would not be adding salt all the time since it would build up.

channel catfish are actually rather sensitive to salt so I would only salt their system to 3 ppt and I only go that high with them if they are experiencing disease problems.

I generally do not salt my larger systems since the sodium and chlorides can build up.  I usually only salt the quarantine system or I might do a salt dip or bath when I move the fish from quarantine over to my larger systems.

Aleece, I started adding salt based on your response to my discussion "Our Fish Dying," posted about 10 months ago. I have continued to salt based on that discussion. My misunderstanding was that I did not need to continue salting the system on a regular basis. So, the salting will stop, unless a problem arises.

Now, will the sodium buildup leach out naturally, or do I need to do a water change or something. Hopefully the plants will benefit from the reduction of fresh salt being added.

John, I think you'll need to change water to get rid of the salt.

sodium and chloride get used up by plants very slowly.  Some plants will do better and use or take up more salt than others, you noted that the swiss chard was doing well anyway, have you noticed the salty taste when you eat some of the raw stem?  Same would likely be noticed with celery.

Since the salt isn't used quickly and evaporation will actually concentrate it, you probably should do some water changes to bring the level down so your plants will fair better.

Salting is NOT something to be done continually, especially in systems where we are not changing out water.

Over the 6 years I've been doing aquaponics, I have salted systems Maybe once or twice per year, and some systems never at all.

With a new system, the chloride ion in the salt can help mitigate nitrite poisoning of fish to an extent through the initial nitrite spike when cycling up with fish.  When getting new fish they are also often stressed and if they are going into a system that is not fully cycled up and experiencing spikes, the salt can also help them some with the stress and help keep their slime coat healthy.  This can be especially helpful for catfish since they have no scales to protect their skin.  However, channel catfish are also very fresh water fish, salt levels of 5 ppt or more could be quite detrimental to them so I only ever salt a channel catfish system to maybe 3 ppt and only when there appears to be a need.

Spinach is another one. It's ability to uptake salt is a good part of what makes it such a good cool weather crop. I'm guessing  the xylem sap is less viscous at low temperatures and flows more freely.

But you really don't want to over do it with the salt, as you may be stressing your plants out at elevated levels. There are some special situations where you would want to do that on purpose to increase degree of brix...but it doesn't seem like that's what you're after...

So you've been adding 10 lbs of salt twice a month for the last ten months? Holy bejesus that seems like a lot. It sure would be kind of cool of you to spend $15-20 bucks on a salt refractometer to see what the salt level is in your system (out of curiosity). It would also be an item that would come in handy for you in the future as well (to keep track of your salt levels)...

If "Salting is NOT something to be done continually" had been mentioned in the discussion last August, we could have been spared a lot of lose and headache. Fortunately we have 550 gallons of water in our rain barrels and this coming week has a lot of rain in the forecast.

Yes the chard has a salty taste. I don't need a salt refractometer to tell you our system is loaded with salt.

Well, can salt continually and regularly if you want... you just need to know how to keep track of what you are doing. ..Nothing I see in that thread indicates that TC suggested you should salt your system twice a month with 10 lbs of NaCl from now til the end of time...On the contrary she warns you repeatedly to "only salt to 3ppt"...

So, you are not the least bit curious as to the actual level of salt in your system? (terms like "loaded' have no meaningful value)...

Well, Vlad, the refractometer is tempting but we have been eliminating the other variables and wondering what could be wrong with the water since nothing else was making sense as to why seeds weren't starting and plants would wilt, wither, turn brown and die so I had looked into a local IFAS/cooperative extension office and they offered to test the water for everything possible for $25 which is something I will consider doing if the water changing doesn't get my plants growing again. We're changing the water, I've sprinkled all the swiss chard seeds I had on hand in the gravel beds and it's the beginning of Hurricane Season so naturally there's lots of tropical moisture to keep our rain chances and totals high for the next few days.  After all that hopefully we'll see some happier plants.  I might try some spinach too since you mentioned it likes the salt but usually spinach doesn't like our warm FL summers so I am keeping my expectations low on the spinach.

Thank you all for your insights, I'll keep you posted on what develops so we can share it with others in this situation.

Just in case you're curious what they would test for here's the form:


an occasional agricultural water analysis is actually a good idea.

The refractometer is a way to actually be able to check salt levels yourself without having to sent samples to a lab and wait a couple weeks for results.  See if you salt more than once, you kinda need to be able to check your salt level to make sure you are not building up your salt higher than desired.

I'm actually rather shocked that your fish are not suffering if you have been adding salt twice a month without knowing what level your salt is at. 


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