Backyard Aquaponics
A place to discuss aquaponics

The salt wont evaporate Rupe

The only way the salt leaves the system is via leaks, and the plants absorbing it.

I have a 4000 litre system and put about 6kg salt in every 2 months and if you measure it now you would only get 2 ppt i have not lost a fish in over 12 months [except the one that jumped] and all the plants are healthy[tomato are taking over the green house]

Never said it would OBO... said that topping up the water each week was the same as doing a water change...

As others have said... yes evaporation tends to leave the salt behind... therefore theoretically a slight increase in concentration...

But AP loses very little by evaporation... 99% is by transpiration IMO... so yep... there is a degree of salt uptake into the plants... and a loss of water

Regardless, whether by transpiration loss or by water change.... the result is the same, or near enough...

Regarding salt concentration...



Gonna have to go all Frank on you Rupe

What you said there, sounds like what it says.

Sooo... if you top up... or do a 10% water change each week... wont the ppt concentration drop over time???.... perhaps it's not exactly a 1:1 correlation ... but IMO it certainly does...

And F&F's experience suggests the same...

A "top up" will not reduce the concentration.

1000l of water at 1ppt, becomes 2ppt at 500l. Adding water to bring it back to 1000l makes the salt 1ppt again.

Obviously, the salt level in the system is lowered by the plants uptake, transpiration will lower the water level, and increase the salt concentration, but adding the lost water back in will bring the concentration back to what it was (minus the uptaken salt).

Top ups wont reduce the overall salt content. Water changes definately will

But isn't it "exponential".. or perhaps "logarithmic".... i.e each time you top up but the same volume % of water you're effectively diluting the remaining water that is less concentrated each time... with me...

And some salt is taken up by the plants via transpiration each cycle... then there's the possible (IMO) combination of free CL ions and hydroxyl ions that IMO have a similar acidifying effect to that of adding muraitic acid... i.e. drag pH...

And some CL ions probably off-gas as well ....

Bottom line is that I tend to run my tank(s) at 1-2ppt constantly.... and probably lose 10% of the tank water volume per week through transpiration... and therefore need to top up....

I regularly test the salinity... and have found that I need to add additional salt about every 4-6 weeks (ala F&F) to maintain that level of 1-2ppt...

And what exactly is the difference to adding 10% of your tank volume as a "top up"... and adding 10% of your tank volume as a water change???....

Granted dumping water through a water change may "lessen" the concentration quicker ... but the same arguement applies.... each time you do it... you are diluting water that is less "salt" concentrated each time....

And no.... 1000 @ 1ppt..... jump 500L.... and you have 500L of water @ 1ppt.... add 500L of pure water... and you want have 1ppt IMO....

Mods can we add GHTGAFOY to the list of acronyms. Or GGFU for short.

Gonna have to go all Frank on you.

I never said anything about dumping water Rupe - evaporation / transpiration.

1000l water, evaporate or transpire 500l, leaves 500l @ 2ppt.

1000l water, remove 500 litre via drain / pump, leaves 500l at 1ppt.

My water loses salinity as well - not from evaporation though.

Cone on now boys [jees its good theres no delite button]

Absloutely!:lol:

Rupe and OBO, you're both right. Shuddup.
Except Rupe, you're not quite as right. Salt doesn't offgas. Salt doesn't get removed by evaporation. Plants are the only thing that removes salt in our systems without water changes.
Topups and changes are not the same thing.

The simple statement "plants take up salt over time" is all you need to say. Anything more complex than that is probably going to be wrong

Thanks Steem... but just to clarify, I didn't say that "salt offgassed" or that "salt was removed by evaporation"....

I said ... "And some CL ions probably off-gas as well ....", and "some salt is taken up by the plants via transpiration each cycle..." ..... and that with the water losses through transpiration (IMO 99% of loss) .... "the concentration will drop over time with water top ups anyway.." ...

A point that OBO agrees with at times (in his own way), but then disregards at others... no matter "Salting" for fish health is a good thing...