Backyard Aquaponics
A place to discuss aquaponics

Greetings!

I've lurked here a few months, this'll be my first time reaching out so, hello and thanks for all the advice I've leeched from you all so far

So I learned too late that fishless cycling is the way to go, if I could go back, that's what I'd do. Oh well...onto the issues at hand.

I have a 100 gallon tank in my backyard and a 10 gallon tank inside. I bought about 40 fingerlings of blue tilapia and split them up (In case I screw up royally and kill off one of my tanks, I have a reserve unit ready to go)

I have 2 planters and am at 50% planter capacity with 30 fingerlings in my aquaponic system. My tap water's ph stays about 8.2 which is what both my system and my tank are at right now. I replaced water like crazy to keep the ammonia down during the first week or so of my cycle (ammonia levels peaked at about .50 ppm) and the fish all lived on like troopers. I added maxicrop and my plants have been thriving.

I'm now in the 3rd week of my system cycle, and my blue tilapia outside are turning black and some have died. I attributed this to nitrite spike, which got up to between 2 and 5 ppm. I added sea salt to get my salinity levels to what I approximate is 3ppt. My current readings are as follows:

water temp: 73 F
pH: 8.2
Ammonia: .25ppm
nitrite: between 1 and 2 ppm
nitrate: 40ppm


The fish in the reserve tank have not grown as big, but look much healthier! They are a bright blue/silver color with distinct markings, are very active and alert. Those readings look like:

water temp: 80 F
pH: 8.2
Ammonia: .25
nitrite: 0 ppm
nitrate: 80 ppm

It seems to me obvious culprit is nitrites, which explain why the fish in my small tank are doing so well where my big tank fish are not. Aside from adding sea salt and replacing water, I don't know what to do to save them. Do I just need to accept the fact that the cycle is going to kill some fish and ride it out, or should I be taking more action?

Thanks for reading!

I think it's probably a combination of stress and nitrites. The outside tank is a bit cooler as well.

Increase the aeration for the outside fish if possible. It may be too late to save them if the damage is already done but I've seen where Tilapia can make it through some pretty bad spikes. The salt should also help and I would also stop feeding and make certain there aren't any dead fish you've missed.

Here are a few possibilities
1. Low oxygen
2. Ammonia
3. Nitrites
4. pH fluctuations due to algae
5. Toxins (like from leaves or galvanized roofing)

Have a look at see which apply

I would drop the ph to closer to six but over a few days
Some salt and a pH of 6 , would.be better FOR TAN...

Thanks for the replies


I think the oxygen levels should be good, I cycle the water every hour, and twice an hour 3 times a day. That should be enough aeration I would think, considering I have two grow beds and I set the drains up kind of high so they splash a bit. I'll post some pictures when I get home...Maybe I'll put an air stone in, too?

Ammonia may be a problem, but I don't think .25 ppm is enough to be toxic enough to kill the fish

Nitrites are likely the problem, I just don't know what to do to get the levels down to manageable level

pH has stayed pretty consistent, and I read somewhere that high pH is good when you have nitrite problems though I could be wrong

Toxins hopefully aren't an issue, I built a screen around my system to keep debris out, and my tank is made of wood and lined with pond liner.


I'll come back today and post pics, I'll check everywhere I can for any dead fish, too.

The nitrite levels should fall as the system finishes cycling especially since you're not feeding at the moment. My guess is that the current levels aren't really the problem and that the damage was done when the levels spiked earlier. Usually when this happens you'll see fish die off in ones and twos over a long period (more initially but it can take a while for all the affected fish to succumb). While you wait and see how this turns out, keep your eyes open for dead fish and remove them.

Once your nitrite gets to zero you can resume feeding and gradually work up the amount in case the filtration isn't fully able to handle it. Make sure not to leave any uneaten food in the tank.

Hope it goes well

At 40°F (26°C) and 8.2pH it's borderline.

I would run constant flood until cycled.

Here are photos of my setup: ( I know it's not 100% optimal, but I am a newbie and am learning as I go

I wonder if oxygen is an issue...I have noticed some dog hairs floating in my tank, I imagine the same thing is happening inside too though since my tank isn't covered at all and my dog sheds like crazy. I do have a filter running 24/7 on the inside tank.

The outside fish hang out near the bottom, I don't see them often near the surface unless I'm feeding them. They aren't gasping for air or anything. You can't really see the outside fish too well, but their color is much darker than the inside fish in the last couple pictures.

I'm going to do some more water replacement, also try and slowly bring down the pH over the next week or so and report back.

Thank you for the replies so far and I am very open to any other advice anyone may have.

**Edit: Oops, I screwed up the attachments. re-uploading.

More photos here

I don't think I'd worry too much about the color of the fish at this point. They can be lighter or darker for lots of reasons and it may be normal and unrelated to the deaths

Thats a relief and good info to have, thanks

As of right now I've cleaned the muck from the bottom of the tank and used a net to catch floating debris after my grow beds dumped, the tank is much cleaner and the fish are out and swimming around, they don't seem as lethargic as they have the past few days. Hopefully this part of the cycle will be over soon and my nitrite levels will go back down to zero. I'll post back in a few days with results.

Thanks everyone for your input so far, I'm very impressed with this helpful community.

Skeggley, if I'm reading your chart right, that means the higher the pH value, the more toxic ammonia becomes to fish?

Too inexperienced to be of much help, but i am wondering what brand your media is, where did you get it, etc? Also are you happy with it?

Hiya, not my chart, copied from this forum. But yes, the higher the pH the more toxic the nh3. Double edged sword as the higher the pH the better for cycling.
Like your set up btw nice work, well done.

Ah, interesting, I didn't know that. And thank you for the compliment!



It's Mother Earth hydroton expanded clay pellets...I got them from a hydroponics shop in my area that generally service a more "laid back" clientele. Some of the pebbles are less dense than water, so they'll try to float if you're over-flooding your grow beds. I also had to wash them pretty well, if you put them straight in without washing off the dust they'll turn your water red.

They provide a lot of surface area and drain very quickly, I am happy with them. I have heard if you let them freeze, they'll expand more, and become very brittle and break easily.

Alright i bought a bag of those online. I dont mind a few floaters as long as the plants dont get uprooted. It does freeze where i live a few times each year on average but it seems like the constantly moving water should discourage milder freezes, especially if i wrap the pipes. Maybe i'll use them in buckets and bring em into the garage when it gets really cold.