Backyard Aquaponics
A place to discuss aquaponics

So over the past 4 weeks, ive lost around 12 fish, which is the first real die out ive had since i started last december.

The only thing seeming that i can detect wrong with the water is low ph (6.5) and practically nil general hardness.

Water temp remains steady between 22 and 23C, Ammonia, Nitrites, Nitrates are very low, ive added a gravity filter to mechanically clean the water as well, and also changed out around 80% of total water over the past 3 weeks.

What should my next steps be?

What sort of fish are you running

Did the water changes lower the PH? Did they die before or after water changes? Have you had lots of rain there?

I have jade perch, silver perch and tandanus, and recently added some freshwater flathead fingerlings. The deaths have been mostly SP and a few JP. These fish have for the most part been in the system since they were 4cm fingerlings, they are close to 15cm now and dying.

The only other thing i can think of is that i recently erected a greenhouse over the tank, mostly to reduce wind. Water change was after the deaths started, it has not substantially altered the PH either.

Water change was partially an accident, I added the gravity filter, which had a pipe come off on its first day, expelling a significant amount of water - took me a week to get it back up as i only had one of my top up barrels full at that point, and needed to leave water to sit to dechlorinate. Also did not want to drop my temp too low, and the tank water is heated, barrels are not. Its been fairly cold outside.

Flathead?

Flathead Gudgeon native aussie flathead.

I should add, theres no visible issue with the fish (other than them being dead).

Also, i did see one actually in the act of dying - i have a webcam in the tank, and essentially it was lying on its side on the tank floor, twitching, None of the other fish appear distressed.

When you say the other levels Are low, what are the readings? You shouldn't have amm or nitrite reading

Sometimes river fish bring in diseases or parasites - how long have the flathead been in there? and did you quarantine them first?

low being nil except for nitrate which is very low. Apologies.
Tested water 0 ammonia, and nitrites, 20 nitrate. Carbonate hardness (KH) around 180ppm, general hardness 30, PH of 6,5

Flathead came on the weekend, deaths started 3 - 4 weeks ago.

Not quarantined, which seems silly on my part - came from an Aquaponics enthusiast - but given they postdate the deaths, not a likely cause, I inspected a departed fish, could not see any indication of disease

Have you or your neighbours sprayed any were near the system for bugs? Ie, pest control operators in the area,

Is anyone close to your system using a wood burning heater or BBQ or stove, some people burn treated wood or pine, the smoke can contain contaminants,

Are there any industrial building up wind from your home?

There are a lot off reasons for fish dying other than just PH and PH can jump depending on your buffer in your system,

Have you tried adding carbon or charcoal bags to your filter, they take out any chemical nasty’s making the water neutral,

I am new to aquaponics but I have raised fish for years in indoor tanks, simple basic things like carbon bags can save a lot of grief,

I hope some of this helps you in finding out the reason for your fish deaths,

Good luck,

The tank is inside a greenhouse, so anything neighbours spray is unlikely to have impact. Will grab some charcoal tomorrow and figure out where I can fit it in the filter.

On further reading, would adding charcoal to my filter reduce the nutrients and minerals going to my grow bed? i pump water from my fish tank through the filter then to the growbed.

Charcoal can absorb heavy metals, and catch minerals and nutrient similar to other media substrates so I can't see how it could assist in any way. Salt to 3ppt and monitor.

Will up the salt content. I may need to get a refractometer.