Backyard Aquaponics
A place to discuss aquaponics

Okay - I think I found the problem but I really need your advice. The short story is that almost ALL of my fish have died. This is an established 2 year old system, but within one month, I went from 30 fish down to only 6! They are dying one at a time, and usually in the morning is when I find them (after waking up from sleeping).

I am THINKING that the problem is definitely related to pH. In the morning, I took this reading showing the pH:



It looks to me like in the morning, the pH is around the 7.4 - 7.8 range.

Now, I just took an evening reading (below), and it looks to me like it's around 8.4-8.8 if I had to guess:



So that leaves me with the following questions on how to MINIMIZE the pH swing within such a short amount of time:

- Would REMOVING PLANTS help with this large pH swing? The theory would be less plants would mean less CO2 pulled from the water which would keep the pH more acidic (and low). Keep in mind I only have SIX small/medium fish in this 110 gallon system, just to give you an idea of what's swimming in there.

- Would ADDING MORE FISH help with the large pH swing? The theory behind that would be more fish == more nutrients for the nitrifying bacteria, which lowers the pH during the bacteria cycle. Perhaps not having enough fish to provide enough nutrients to the plants is causing these high pH swings during the day.

What are your thoughts based on the above chemical readings?

Be sure that your viles are clean and rinse them out in the fish tank water at least three times before you add chemicals and do your readings. Be very careful to follow the directions carefully. Contaminates or the wrong number of drops will make the readings wrong. Double check if it does not look like you think it should. Also check you top up water so make sure it is about the same PH as your fish tank. Let your top up water set about 24 hours to make sure you get the correct reading. some times it changes when it sets. Good luck with your system.

Yeah... there's absolutely no reason for a pH swing of that magnitude to occur within 12-24 hours... even if you have a lot of algae...

Do you have a lot of algae....??

How are your other water parameters?

Hey guys, thanks for the response. My other measurements are fine (ammonia/nitrites/nitrates). No algae of any kind since my system is inside a black stock tank with full shade during the day.

My current theory as to the problem has NOTHING to do with ammonia, or disease (although I agree that some fish may be fighting some kind of illness due to the past issues). My current theory is that my fish are slowly dying from these large DIURNAL PH SWINGS.

You see, I NEVER considered to check PH twice a day, nor did I know that pH could swing so wildly in a 24 hour period. It appears that my pH was swinging more than 1.0 point, from the high 8's to the low-mid 7's. That meant that at night, when the water was very alkaline, it would change to very acidic in a matter of 10-12 hours. I think this may have been the main cause of either KILLING the fish outright, or making them sick and weak to succumb to something else later on.

MY MISTAKE - I assumed that three powerful grow beds returning water to the tank would be enough "aeration" to prevent these large swings. Apparently, I may be wrong about that. So last night, I went out and purchased a 4-line air pump, made for 170 gallon tank, and I put all four lines into the tank at full blast. From my research, it says that AERATION will help minimize large pH swings.

I never knew that! So here's where we stand. I am currently aerating the CRAP out of my water. I have that new air pump running 24/7, in addition to the 3 grow beds returning the water during the siphon cycle, and my Radial Flow Filter constantly pouring water back into the tank as well.

We will see if that will minimize the pH swings and help the fish.

That's where I am right now. I don't know if the pH swing was the initial cause of all these fish deaths, but I do know that it's a PROBLEM regardless, and it needs to be corrected. That's my focus right now and I will keep you posted on how it goes. So far, this morning I had no dead fish (although I'm only down to 5 in that main tank).

What kind and size are your fish? 110 gallon tank might have been too small for the number of fish. Got pictures????

Right now, I only have four koi (small to medium size juveniles), and a few goldfish.

In the hayday, I had just under 30 fish (mostly goldfish). I think it was a perfect storm of things that happened. The slow build up of CO2, leading to wide swings in pH, that's what I suspect began to kill the fish, one by one, over a period of a few weeks. Unfortunately, I didn't know about pH swings, so I was mainly focusing on issues with ammonia, nitrites/nitrates, or some invisible bacteria causing the problem.

I don't have any pics right now, but here is a video from two months ago (before any fish died and all were apparently healthy):

http://www.youtube.com/watch?v=mOajrsoR0yI

As you can see, the fish were very social and plentiful. I think the system (after two years) may have reached a critical mass of growing fish + poor water quality and it wiped about all of them out.