How to handle Potasium/ Calcium supplimentation when Ph never goes below 7.4

[Richard Kowalski]

Hello Everyone,

This is my 7th year running my Aquaponics system. This is the first time I have run into a problem where the Ph has been hovering between 7.3 - 7.6 for the past 4 weeks. I built a hybrid system that consists  of a 300 gal fish tank. The fish tank has 80 Tilapia fingerlings. The system also has 3 Deep Water Culture  bins where I grow lettuce and 2 grow beds with hydroton growing Bok Choy, Peppers, Cuccumbers, Tomato's, Basil. The entire system is in a hoop house that gets shut down and cleaned out roots and all in the winter because its just too cold and not cost effective to run it year round in New York. The only thing I am doing differently is that this season I have planted alot more plants than I have in previous years because of the amount of Tilapia I am raising. I start all my plants from seeds indoors using Rockwool. There is alot more Rockwool in the system. The first thing I checked for is fish deaths. The fish are fine. The Tomato plants and Cuccumber plants have shown signs of Chlorosis. I tried using a foliar spray of Potasium Carbonate and burned my plants. Luckly I only lost a few of them. I have supplemented Chealated Iron first to see if that would solve the problem. No luck. Thats when I tried foliar spray of Potasium Carbonate.

What have you done to suppliment Potasium , Calcium with such a Ph? Why do you think the Ph is not falling like it should? Water temp is in the low 70's. Its heated. Ammonia and Nitrite is 0 ppm.

Thanks for your time and comments.

Rich K

[Jeff S]

It's been a while since you posted. I'm surprised no one has replied. If your ph is 7.4 it's too high for good plant growth as you probably know. I have a similar problem and similar system. I use muratic acid to lower ph in low doses. You can lower the ph to say 6 and dose with potassium hydroxide and lime to raise it a little while supplying your nutrients or you could use potassium sulphate and calcium nitrate to just add nutrients. Skip the lemon and lime juice for lowering ph. Muratic acid is cheaper and faster.

[Rob Tolette]

Hi Richard,

You can try adding a product like Aquaponic Elements into your system.  Among other nutrients, it contains potassium, calcium, and iron. You just add it to your sump tank and it dissolves in over time.  Dropping your pH should help a lot as well.  I use phosphoric acid, which is in products like AquaDown.  It's probably taking a while for your pH to drop if you have a lot of buffer in it, like calcium for example.

What are your nitrate levels?

[Richard Kowalski]

Hello Rob,

My Nitrate levels always run very high. No matter what I do. I use the API test kit. The Ph problem seems to have fixed itself. 

I have been adding M1 Biological but I dont know if it is making any difference. Its September and the garden is winding down. I close the greenhouse in December because it is too expensive to heat the building and water on Long Island. I start up the greenhouse again in March.

Thanks for your input!

[Alex Veidel]

Hey Richard. As far as the nitrates go, yeah, I've been there myself. I take it they are pretty much off the charts and testing at a beautiful ruby-red color? At that point, you can do partial water changes until you get your nitrates down, but I find that to be much too much work. I prefer to transfer the fish to a separate container filled with system water and a good amount of supplemental air while I drain, replace, and treat the remaining water back to where it should be. Once I've got matching pH levels between the fish container and the rest of the system, I go ahead and add them back in.

If you're using well water and if you don't have one already, I would go ahead and invest $8 in the API KH test kit for freshwater: https://www.amazon.com/API-TEST-Freshwater-Aquarium-Water/dp/B003SN...\

The pH issues you had earlier might be a result of high carbonate hardness (KH), which acts as a pH buffer. Your pH won't lower until whatever acid you've been adding neutralizes all the carbonates in your water. This can take a good bit of acid if your source water is high in carbonates (mine tests at 18dKH), so use the cheap muriatic acid you find at your local hardware store and save your $20 bottle of phosphoric acid for minute adjustments.

[Tom Oliphant]

I add about one tablespoon of a micro-nutrient solution (that contains Potassium and Calcium) about once per month. It and Chealated Iron seem to work for me to avoid the yellow tint. I have noticed that an inadequate amount of CO2 will cause what looks like Chlorosis.

My pH hovers around 7.2 and 7.6 but it doesn't seem to damage the plants. One source I have read says that plants like pH between 6.5 and 7.0 but I guess they can get used to some deviation.

TVO >:)

[Jeff S]

Actually most plants like closer to 6.0. Nutrient take up is hampered by ph as high as you are running. In theory a properly running system will require regular raising of the ph. This is where I use potassium hydroxide and lime which also supplies potassium and calcium. Seems like for the first couple of years my ph stayed high so I eventually added some muratic acid to the system and the ph stays lower now.

[Tom Oliphant]

Thanks Jeff. I will see how it goes. I am noticing a very gradual lowering in pH as time pases. My real question is which test to believe. The API water test kit that I got from The Aquaponics Source measures pH of my 500 gallon fish tank to be at 6.4. The pH meter that I bought and calibrated with a known test solution packet at 4.0 shows that the meter is 0.14 off of true. The meter shows that my pH fluctuates between 7.3 and 7.5. That is a whole unit of pH different. Who do you believe? I also use a general pH chemical set that I bought from the local hydroponics store and it shows that I am stable at 6.5. I don't know what to believe but I have more confidence in the meter that was engineered for accuracy +- 0.01. What do you think?

TVO >:)

[Daryl Leven]

Tom I live in TN and the water coming out of the tap has a pH of 7.4 - 7.6. I have used pH Down to lower the pH, but have been unable to hold it at 7.0. I run a 200 gallon system, with 4 media beds and a 12 foot long DWC. I have 25 tilapia in the fish tank and they are about 3 months old. My ammonia is a little elevated, but my nitrites are at 0.0 and nitrates at 10. I also have found a difference between my portable pH meter; my Blue Lab meter, and the API test kit when it comes to pH. The difference is small between the portable pH meter and the Blue Lab meter but about 0.3 points between the electronic meter and the API test kit. Since the difference is not that large, I am not worrying about the variation. I continue to tweak the system to maintain the pH as close to 7.0.

Tom Oliphant said:

Thanks Jeff. I will see how it goes. I am noticing a very gradual lowering in pH as time pases. My real question is which test to believe. The API water test kit that I got from The Aquaponics Source measures pH of my 500 gallon fish tank to be at 6.4. The pH meter that I bought and calibrated with a known test solution packet at 4.0 shows that the meter is 0.14 off of true. The meter shows that my pH fluctuates between 7.3 and 7.5. That is a whole unit of pH different. Who do you believe? I also use a general pH chemical set that I bought from the local hydroponics store and it shows that I am stable at 6.5. I don't know what to believe but I have more confidence in the meter that was engineered for accuracy +- 0.01. What do you think?

TVO >:)

[Jeff S]

I use the API kit. I've used ph meters in the past but the calibration isn't stable enough for me. The problem with the API kit is that it doesn't go lower than 6.0 so when it's yellow you don't really know how low it is so I just shoot for a little green.

[Kurt Fischer]

Hi fellow Aquaponicers,

I,m I newbie in Charlotte,Vermont , water temp is set at 70 my tomatoes are blooming, but the older leaves  are starting to show some intervenal clorossis . I have added cleated iron witch got everything growing like crazy now I'm thinking it is potassium but I don't want my ph any higher . Is potassium sulphate a good choice?

current ph 7.2 Amonium .2 ppm nitrites 0ish nitrates 50 ppm

system is housed in a 13'x 30' well insulated building with insulated glass on 1 side , a 6 kw array on the roof that powers my house and the greenhouse 2 x 500 gallon fish tanks with 150 bluegill and a few yellow bulhead and 6   3'8 x 5' DWC tanks. The whole building rotates on a central bearing to track the sun. This time of yr it is heated with 1 4500 watt water heater element in a reservoir on thermostat using some of the excess kWh generated in summer months with a 30 below wind chill all night the air temperature is 60.

This is a clip I sent to some friends on Christmas morning I talk a bit about the making of the project. https://youtu.be/gnPaUb7zH6M
This one shows the latest growth
http://www.youtube.com/watch?v=Lsw9QQ1rFLw

Thanks for any advice, Kurt 

[Jeff S]

You have quite a unique system there. Pretty extreme for a newbie LOL. Potassium sulfate will be fine for your system. You really need your ph around 6.5. You can add a small amount of muratic acid and that will lower the ph. Go slow, it works fast. Check out Nate Storey on the Bright Agrotech channel. He has many videos covering all aspects of aquaponics. No nonsense info.

 

Kurt Fischer said:

Hi fellow Aquaponicers,

I,m I newbie in Charlotte,Vermont , water temp is set at 70 my tomatoes are blooming, but the older leaves  are starting to show some intervenal clorossis . I have added cleated iron witch got everything growing like crazy now I'm thinking it is potassium but I don't want my ph any higher . Is potassium sulphate a good choice?

current ph 7.2 Amonium .2 ppm nitrites 0ish nitrates 50 ppm

system is housed in a 13'x 30' well insulated building with insulated glass on 1 side , a 6 kw array on the roof that powers my house and the greenhouse 2 x 500 gallon fish tanks with 150 bluegill and a few yellow bulhead and 6   3'8 x 5' DWC tanks. The whole building rotates on a central bearing to track the sun. This time of yr it is heated with 1 4500 watt water heater element in a reservoir on thermostat using some of the excess kWh generated in summer months with a 30 below wind chill all night the air temperature is 60.

This is a clip I sent to some friends on Christmas morning I talk a bit about the making of the project. https://youtu.be/gnPaUb7zH6M
This one shows the latest growth
http://www.youtube.com/watch?v=Lsw9QQ1rFLw

Thanks for any advice, Kurt 

[Kurt Fischer]

Thanks Jeff, new to Aquaponics not building, now retired from 35 years as a self employed contractor.

it was and is a fun project,lots of keeping my brain busy with research ,designing and building.

do you have pics of your setup you would share?

thanks again, Kurt 

Jeff S said:

You have quite a unique system there. Pretty extreme for a newbie LOL. Potassium sulfate will be fine for your system. You really need your ph around 6.5. You can add a small amount of muratic acid and that will lower the ph. Go slow, it works fast. Check out Nate Storey on the Bright Agrotech channel. He has many videos covering all aspects of aquaponics. No nonsense info.

 

Kurt Fischer said:

Hi fellow Aquaponicers,

I,m I newbie in Charlotte,Vermont , water temp is set at 70 my tomatoes are blooming, but the older leaves  are starting to show some intervenal clorossis . I have added cleated iron witch got everything growing like crazy now I'm thinking it is potassium but I don't want my ph any higher . Is potassium sulphate a good choice?

current ph 7.2 Amonium .2 ppm nitrites 0ish nitrates 50 ppm

system is housed in a 13'x 30' well insulated building with insulated glass on 1 side , a 6 kw array on the roof that powers my house and the greenhouse 2 x 500 gallon fish tanks with 150 bluegill and a few yellow bulhead and 6   3'8 x 5' DWC tanks. The whole building rotates on a central bearing to track the sun. This time of yr it is heated with 1 4500 watt water heater element in a reservoir on thermostat using some of the excess kWh generated in summer months with a 30 below wind chill all night the air temperature is 60.

This is a clip I sent to some friends on Christmas morning I talk a bit about the making of the project. https://youtu.be/gnPaUb7zH6M
This one shows the latest growth
http://www.youtube.com/watch?v=Lsw9QQ1rFLw

Thanks for any advice, Kurt