Backyard Aquaponics
A place to discuss aquaponics

So i had a round of fish deaths over the last 6 months which i can't seem to solve.

i've lost all of my koi to it now so i'm fairly frustrated and looking for a silver bullet at this point.

the fish seem to die one at a time with the following sequence.

1. they become lethargic
2. start gasping at the bottom of the tank
3. sometimes red patches are visible
4. sometimes they develop the classic dropsy pine cone shape
5. sometimes they start having swim bladder issues and float upside down

i have noticed some flashing as well.

all of them die without fail once they start gasping, although i had a couple which just went belly up without any warning. all of this seemed to start when i moved the fish from their pond into the new setup, which ironically is far superior in water quality, aeration and filtration. i gave all of the fish a salt bath when i moved them as well.

i have tried dosing with 3ppt of salt, baths of permafix, removing the sick fish, water changes.

water tests show ammonia 0 nirite 0 nirate 0 PH 6.8

my googling leads me to believe it is some kind of external parasite such as costia.

so all of my large fish have carcked it but i'm not going to give up, my plan is to sterlise the system and i wouldn't mind some feed back on my plan.

step one is to isolate the silver fingerlings in a 20L tub with aeration and salt it to 3% and leave them there for 7 days. i also plan on giving them some 30 minute baths at 6% salt as well. i'm going to leave the tub out in a warm spot as well as my reading leads me to believe most parasites can't take warmer water.

step two will be to drain the tank and grow beds completely and allow them to dry out for the week. then i will wipe down the tank with a 15% salt solution to nuke the hell out of anything trying to survive.

step three is dealing with anything lurking in the beds or pump. i was going to use the same 15% solution in 100L of water in the tank and cycle this through the pump and grow beds for 30 minutes before diluting it away by filling up the tank again with fresh water.


i'm a bit unsure about the growbed part, i don't want to kill all the plants and worms if i don't have to - will fish parasites survive being dried out and not having a host for a 7 days? is 15% salt too much and could i safely use less?

What are your temp swings like?
It sounds like your system is pretty small

it's a 1000L system - the 20L is just a holding tank

1KL isnt a big system. - when i said small, i meant if you can dillute 15% salt in 100l down to 3% with just top up water, it doesnt sound large.

what are your temp swings like?

i had alot of problems with temp swings - much bigger system than yours too (was 5kl at the time) - at the start and had constant and slow deaths, much like you are getting.
a couple of other people who have posted the same sort of thing.... it sounded very much like that was thier problem too.

It took me many months and blaming many different things to narrow it down to temp, if you are getting more than say 4-5c swing throughout the day and night, i would hold this as the first possibility.

is that going to cause bloody fins, flashing and dropsy though?

changes in the season do seem to correlate to it though i'll give you that much. the first deaths happened in april when we had that unseasonable hot weather.

It wont correlate with anything except very stressed fish.
When i say check your temp swings, dont think that i am saying that your fish are "cooking or freezing"......
they get stressed by it, very stressed, so any other little bacteria/infection or any other problem you can think of has an open door......

When i had fish deaths, i even managed to kill goldfish, *frack* goldfish!! Some of them had flesh rot..... flesh rot!
You cannot simply blame a disease, there has to be a reason that disease took hold, especially since you say you took them from a pond where they were obviously doing well, you had healthy fish, you put them into an empty tank, now they arent healthy.,... there is something there and i wouldnt blame it on disease alone, which has supposedly come from nowhere?

You just have to check every possibility.

Also, avoid things like permafix if you want to eat from the system.

i never put permafix in the system, only as a bath outside of it and only on non edibles.

the fish weren't doing "well" in the old pond hence part of the reason for the move, i could see red patchs on them and the ammonia was too high due to a lack of filtration.

it seems a bit of a long shot that the water is changing 4 - 5c in a day but i'll take some readings and see before i do anything.

how did you fix it in the end, insulation around the pond or something?

I used to run "NFT" pipes - really 100mm stormwater pipes - with bioballs in them instead of using netpots.
This lead to very slow water flow and lead me to having to have them as flood and drain.
having 12 x 6m pipes filled with rocks heats up pretty quickly, so when the next flood cycle come it then took all that heat back to the tanks. My pipes are on a flat tin garage roof, so very exposed.

Once the media was removed and the water didnt hang around in the sun for as long it didnt get so hot.

Simply put, dont use media filled "nft" pipes.

4-5c swing between lowest night and highest day temps actually probably isnt that big, i think i still can get a couple of degrees swing with having about 11000L in the system now. I cant remember exactly, but i think i used to get closer to 10-15c swing in summer when i had the tubes filled with media.

my growbeds are about 50cm deep so i don't get much exposure to the sun from the media and the pond is 1/2 shaded by 1pm.

I want to move the growbeds around anyway so now is my chance

update on this, i'm 99% sure it was parasites. i salted my system to 7ppt and it's been 3 weeks without a death.

unless you count the plants