Backyard Aquaponics
A place to discuss aquaponics

Trying to tie different aspects of aquaponics together and get a clearer picture

plants (depending) have their own preferred pH range
EG
Basil 6.2 - 6.8 , Lettuce 6.2 - 6.8 , etc...

Fish have their preferred pH range as well
in my case tilapia prefer 6.5 - 8.0

So here is the question, what is correct range to have your system at ?

From what I can see 6.5 - 6.8 seems to be the best for many types of plants
and 6.5 - 6.8 seems to be on the low side of the preferred side for tilapia

Is this correct or am I missing something key ?


Also is, it best to have a storage tank of water that you adjust the pH level to that you want in your system and then when needing to top up or add water, you add from the tank. Thus you can control the "fresh/new" water going into the system. Is this advisable ?


Thanks in advance

You pretty much have it. While a tank, as you suggest,would never be a bad idea, I'd say it's only necessary if your top up water needs to be adjusted (e.g. You're using hard water).

thanks scott_dc
Yes I sadly do have hard water 228 mg/L hardness or 80.71 ppm Calcium

Tank is probably a good idea then. With pH, the specific value is often not as important as not having sudden changes.

>> From what I can see 6.5 - 6.8 seems to be the best for many types of plants

6.5 to 7.5 is generally optimal for plant nutrient uptake. Most AP systems run OK in the 6.5 to 8.0 range, though high GH/KH can be an issue for some nutrient uptake/lockout. eg. at higher pH choice of iron inputs need consideration (well discussed around forum).

Scott_dc nailed it with the consistency comment - it is worse to have a system that is constantly changing.
So having a tank on the side means that you can basically ensure that water going in to the system matches the system.
Rainwater helps a lot as it is naturally slightly acidic, but too much with moderate-high system nitrates can cause the system to crash the other way (to 6 and below) and you will end up having to add some form of pH buffer. Topping up with water slightly above your desired pH is not a bad idea - eg. 7.2-7.6

If you are going to acid treat your water (usually HCL) then really should be doing it on the side.

The average pH value should be 6.8 to 7.2. If this value increases, then the plants or fishes can die.

When I first installed my system, I was (and still) using scoria. Scoria pushed the pH to 7.8 but the normal acidification of the system pulled it down to 6.5 and below in about 5 months. There was fish all that time

Yesterday when I finished carrying the grow beds for my mark II design, I checked the parameters to move the fish from FT to sump temporarily and it was 5.4 (yes I know, I am shocked too and calibrated the pH meter and checked again). Fish seems normal and no casualties so far (touch wood) and I don't know for how long it's been like that as I wasn't testing the water for a while.

I am now dangling about 10 oyster shells in a net in my sump. This will be a slow adjustment.