Backyard Aquaponics
A place to discuss aquaponics

Been a long time lurker trying to absorb as much information as I can from this site. But I have run into a problem where I am losing a few fish and I can't figure out why. Firstly the background.

I have an in ground 1500L pond with 3 large Koi, 1 baby koi, 5 largish comets and approximately 10 eel tailed catfish. They have been happily co-existing for months. The pond is connected to a 20L commercial pressure UV filter as well as a 150L barrel DIy swirl barrel filter. The water cascades back down into the pond for aeration. I have four 1/2 blue barrel GB also attached to the pond. The entire system is fully cycled. I generally keep the pond at approx 1ppt salt.

I generally feed the fish twice a day, once with koi pellets and once with sinking grobest barramundi pellets (which is what my silver and jade perch in my double UBC system eat). They generally polish off all the food extremely quickly. Approximately a month ago, the fish seemed to go off their food. They would still eat (as in the food would disappear eventually) but basically a fraction of what they would normally eat.

I tested the water and ammonia, nitrite and nitrate was basically 0. The only thing wrong was the ph which was registering as 6.0 (kit doesn't go lower than that). I gradually brought the ph back up to about 6.8 using Ph-up. The water has been crystal clear as it has always been.

Over the course of the last few weeks, the baby koi and 2 of comets have died. In the meantime, I have done 2 consecutive 30% water changes, cleaned the barrel filter and pressure filter. The barrel filter gunk smelt swampy and I flushed all the gunk out. The pressure filter was full of a colony of snails as well as dragonfly larvae (also dead ones which get trapped in there). If the water quality was bad I would have thought that the snails would be the first thing to die.

Since I cleaned everything, my largest koi has now also died. All the fish have shown no signs of injuries, sores or disease. The eyes are clear, fins in good condition. I opened up the koi and it seemed totally fine, lots of body fat, a large egg sac, gills were good.

Basically I am completely at a loss as to what the problem is. Clearly there is something wrong but it isn't anything that I can put a finger on. I have since removed the 2 remaining koi and 3 comets into my double IBC system. I have left the catfish in the pond and salted to 4ppt.

Anyone have any ideas because I sure don't.

The pH dropping could have triggered something to do with metal leaching into the system. Are there any metals other than high quality stainless steel in contact with the water anywhere in the system? Zinc and Copper become much more toxic to fish as the pH drops and they also tend to leach into the water more as the pH drops.

Most of the "unexplained" fish deaths seem to come from metals leaching, other chemical contamination (did a neighbor spray any pesticides or herbicides lately?) Changes in source water (is your top up water now being treated with too much chloramine instead of Chlorine so now just aerating it doesn't take care of the problem?)

Or, I suppose it's possible your filtration (swamp stink) could have been a sign that you had something nasty like hydrogen sulfide building up in your system which can be bad for fish too if it or other anaerobic decomposition gas gets back to the fish without being degassed out of the system. If this is the cause I would say clean filters more often and add extra aeration especially near where the water returns to the pond from the filters.

Sorry to hear about the fish. I heard ph up is not good for fish, but I've never used it to have a valid opinion on this. i keep coral rubble on the bottom of my filter.

Post some pictures would also help

There has been no change to the basic setup for months. There is no metal in contact with the pond. I've attached a photo of the pond (I've 1/2 emptied the pond and will do a water change to try and completely flush the water). Unfortunately I didn't take any photos of the dead fish but as I said, they all looked completely normal, no signs of stress or disease.

If a neighbour has done some spraying I am not aware of it, though it is always possible. The other system is also nearby and whilst the tanks are covered the GBs are not. That system seems to be totally fine.

I used ph-up because I wanted to raise the ph and didn't have any other options at the time. I have since purchased some oyster/shell grit.

The top up water is either rainwater (from a small tank) or tap water. The same water that is used to top up my other system. I left the tap running overnight in the double IBC system the other day and managed not to kill the fish!

The odd thing is the large koi died almost a week after I cleaned the filter so you would think that isn't a cause. By that stage there would have been an approx 50% water change as well.

I wondered whether the rhubarb plant in the BG might cause problems but I wasn't able to discover anyone that has had problems with rhubarb in aquaponics.

I also wondered whether the high protein barramundi feed might cause problems but all my fish have been eating it for months without problems.

So far the fish I have transferred out of the pond are all still alive. The catfish don't seem to have been affected at all. The annoying thing is that I haven't done anything different for this pond compared to the other system. Bit hard to know what to do when I don't know what the problem is! Grrrr!

I would check with your neighbours if anyone has had a pest contoller in the sprayover could have had an effect.

The feed would be a problem if it was old or moist and spores had developed which you could not see.

Check the bottom of the pond to ensure nothing has been thrown in.

Filters becoming anaerobic or overloaded with organic matter can cause problems and it i possible that things had gotten bad and after cleaning that sometimes stirs things up before they get back to normal.

If it has only been Koi and goldfish that have died but not the catfish, it makes me wonder if maybe it does have something to do with the feed or time to look for problems that affect the carp more than the catfish?

Good Luck deciding on an answer, it always sucks when the deaths are unexplained and you can't figure out what to do to make things "right again."

You mentioned rain water.Have you got any zincalume or galvanized roof or gutter?I had a plastic cover on the Green house and a zincalume gutter and that was the problem I had ,just one dying here and there.Since I lined the gutters with plastic I don't have the problem.My house tank has a zincalume roof gutter and tank .If I take fish out of the stinking water in the creek and put them in some of that they all dead in an hour.We think we are doing the right thing with rain water but I think more fish are killed with it than any other sort.

Good Point there dbird! (well it isn't so much the rain water directly but how it's caught and collected.) Acidic rain water is able to leach metals fairly effectively and galvalume, nicalume or galvanized metal roofing, gutters and tanks are quite capable of leaching toxic levels of zinc into the water they catch and hold. I made a point of coating my metal roof with a potable water complaint elastometric coating before starting to collect rain water for my aquaponics system. The white elasometric coating also has the benefit of keeping the inside of the house/barn a bit cooler and helping seal up the leaks we had before.

The second I saw rain water, bells went off for me too. I have seen quite a few fish kills due to collecting rain water off of unsuitable surfaces.

I think the high protein diet and lack of fiber might be the answer to their death, specialy since it's been wrong diet for month's

cut/paste from here : http://www.fishhelpline.co.uk/health/food_feeding.html

....... However, 95% of Koi over 28" die of fat degeneration of their internal organs. There are many reasons for this - poor grade food which is corn based is one, an other is high protein levels in their early stages of life, which damages their liver and kidneys but does not show its self until the fish is around 3-6 years of age.......

........Under no circumstances feed trout pellets to Koi or sturgeon, unless you you want to kill them with catarrh of the intestines (dysentery). The pellets pollute the water....................

cheers

I don't know much about Eel taled catfish but I know that channel catfish over here in the US actually need even less protein than tilapia and since the catfish in the pond system don't seem to have been affected I wasn't sure if the high protein/fat diet would be the problem for the Koi/goldfish/carp types?

I had also not been sure on the metals thing since I also would have expected the catfish to show problems before the carp types?

Are Eel taled catfish know for being really tough under all sorts of conditions including metals in the water and extra rich feed? Or might it simply be that the Koi are older and simply dieing now of too rich a diet for a long period of time?

Well my roof is terracotta tiles and my gutters are copper. I am aware that long term contact with copper (say a copper tank or copper heating element) isn't good for fish but I wouldn't have thought that momentary contact with the gutter wouldn't leach enough into the water to affect the fish. My rainwater tank isn't big enough that I can top up using rainwater alone, typically it is a mix of rainwater and tap water. Generally I also pump out water into the garden when doing water changes so there shouldn't be a build up over time. Additionally, this is the same water that gets used in my other system.

In terms of feed, I have always fed my koi and comets proper koi pellets. Approximately 4 months ago I put in the catfish and fed them the barramundi sinking pellets. Of course invariably the koi would come along and help themselves as well. But they have never been fed exclusively on the sinking pellets.

All my food is stored in a chest freezer and I take out packets as required so I would be extremely surprised if the food is off.

The thing is that I noticed a specific change in behaviour with the fish where they went off their food pretty much overnight. That kind of suggests to me a specific change or event. Whether I can isolate what that change is who knows.

Anyway, I have basically done a 80-90% change of water in the pond and put the koi back in....let's see how they do.

All my goldfish died recently in similar circumstances. Over a period of a week, they went off their food and all 10 goldfish died, one day at a time. Until then they were eating voraciously and getting larger, eating much more than all the silver perch combined.

The 40 odd Silver Perch that were in the same tank were fine - in fact, they are still fine months later.

I didnt care about the goldfish dying as they were just starter fish, but did want to know what the problem was in case it was water quality or disease related. I guess their biology is similar to koi carp.

Given the Perch had no problems, I think it was something to do with the high protein food and how much of it they were eating. The goldfish were real gutses and swam around developing huge bellies while the silver perch were still skittish and getting used to their new home. From what I can gather, excess eating can kill koi and goldfish as fat can develop around their organs (as it can with humans I guess).

I really hope eating lots doesn't kill my silver perch, I've been experimenting the last few days to see how much I can get them to consume in this hot weather.

Maybe get a copper test kit? The copper might not build up over time because you empty into the garden but it could very well be building up in the fish.

My eeltail cats have been hale and hearty from day one and in that time I have had 4 silver perch die from mysterious causes. I'd say the tandanus are tough little buggers.