Aquaponic Gardening

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I have had some issues the last few days. I have developed poor pH testing habits and failed to see my pH drop below 6. I was using an electronic meter to test samples of water in 5mL test tubes. I would submerge the meter into the test tube until it sat on the bottom. I believe the meter was reading the pH of the glass rather than the aquarium water. I say this because when I cross referenced it with the pH test dye I got staggeringly lower results.


 I have started to see fish die off one by one over the last 10 days. I added 20 more fish after balancing the pH back out with some pH Up (potassium hydroxide).  I saw a few more fish die off in the last couple days. I am now down to 30 goldfish. I am  disappointed by the loss of 10 fish. I know goldfish have a reputation as being junk fish but it is always a bummer to see them mysteriously die. I attribute the deaths to the drop in pH and subsequent balancing as well as from the introduction of new fish into the system.


I am going to use the dyes to determine my measurements from now on. Live and learn I suppose.


The veggies are doing great! They have grown quite a bit. I'll tell you all about them next post!

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Comment by TCLynx on February 1, 2011 at 1:06pm

Shell grit, you can get a small bag of it from most any feed store (Tractor supply sells it.)  People feed it to their chickens to provide supplemental calcium to help keep the shells strong while also providing grit to help the chickens grind up the food.


Busted up oyster shells is a common form of shell grit.  Sometimes they sell limestone chips instead.  The shells will usually buffer to about 7.6 while limestone could cause the pH to go even higher than that if too much is added.

Comment by Sean Short on February 1, 2011 at 12:54pm

My pH is about 7.2. Thats a rough estimate because the dyes are based on color matching. Basically I am at a a lighter color than indicated by 7.6 but not quite to the color of 7.0. From my understanding the best pH is around 7.0 so I am going to allow the nitrification process to lower the pH. I like the idea of using a base like your shell grit. I have no idea what that consists of though. or where something is available. I would much rather use something natural than having to add CaOH or KOH. 

Comment by TCLynx on February 1, 2011 at 7:31am

Well what is your pH now?!  Changing it in one hour could definitely account for the fish deaths after the change.  Gold fish are generally pretty tough but they can still be killed.

.25 ppm ammonia is not cause for panic but once a system is cycled up, we would prefer that it be balanced such that the ammonia and nitrite readings are 0 ppm or as close to it as possible.

It is kinda hard to know what is going on without tests before and after the pH change.  If the pH had only dropped slowly and was only below 6 for a very short time, the bacteria may have survived and are working.  I would advise doing regular tests here for a while to see if the ammonia drops back to 0 or if it starts rising?


In general when adjusting pH, we want to move it only .1-.2 per 24 hour period but I know this can be really difficult which is why I tend to try and keep my pH above 6.5 by hanging a small mesh bag of shell grit in my system.  If the pH starts to get too high I pull the bag out and if it drops too low I put it in or add more grit to the bag.  Shell grit or limestone is slow acting stuff so one must not wait till the pH drops too much to use it.

Comment by Sean Short on January 31, 2011 at 8:12pm

TCLynx -

Thanks for your comments.

So I tested for my ammonias, nitrate and nitrite and those all seemed to be in par. nothing wildly different from other days. I did also shoot the pH back up in less than an hour. Probably not good when I think back. I hear what you are saying about cycling the bacteria back up. How will I know what damage I have caused to the bacteria culture? If my ammonia levels were around .25 ppm after I adjusted the pH is that a good or bad sign? I have such limited time w/ AP that I default to my years of hydroponics experience. I have since gotten better testing habits and rely on the test kit dyes rather than electronic meters. 

Comment by TCLynx on January 31, 2011 at 5:46pm

There is more to it than just the pH.  You also need to be monitoring ammonia and nitrite after a pH crash like that since you may be having to cycle the bacteria back up.  The fish were not dieing from the low pH but rather probably from high ammonia levels when you adjusted the pH back up.


electric pH meters still need calibration and proper cleaning/storage and they can fail too.  It probably was not the glass you were measuring it was probably that the calibration had gone off or the meter just quit on you.  Some of them have replaceable probes that only last so long.

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