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Cakoi

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Hello from the tropical Vietnam. I’m sorry admit i’m quite ignorant about pond keeping because although i have a koi pond for 4 years, i’ve mostly never had sick fish, thanks to an undesirable setup. More on that below. That changes today, and i’m suddenly stressed and very worried.

My 13 m3 outdoor hard walled pond in Vietnam is filled with a 2-ft thick sand at the bottom. It has a tiny biological filter, no UV, and a very low circulation pump rate_ I couldn’t do anything to change it. For 4 years, the filter system works very poorly. Pond water was mostly muddy or algae cloudy, with only a few short spans where the water was kinda clear. The ecology of the sand bottom layer didn’t filter the water as i had hoped.

Because I cannot change the filter setting without the huge cost of breaking and rebuilding the pond, I resigned to keep 4 fishes only. Apart from the visibly unclear water, the fishes live ok. I guessed the nitrite, nitrate and problem of overcrowdedness, overfeeding is not applicable here.

Last month, I changed the position of the filter j mats inside the biological filter. Miraculously, the water became very clear. It’s nowhere near the clarity in those black-painted hard bottom ponds with big filter systems as populare here, but this was beyond my expectation. It’s clear, it’s beautiful and looks healthy. I was so happy. About a week before the reshuffling of J Mat, i introduced a new batch of 5ea 20-cm new kois to the pond.

But recently, for about 2 weeks now, my bigger fishes don’t want to eat much any more. They also tend to stay motionless for most of the day. Because my pond is shallow and spread out and the water flow doesn’t create any water current, my fishes were never forced to move much for years. They are shy and usually find quite spots to stay idle. But now they are even more ‘resting’ than before.

Also recently they seem to do more flashing. I liked to think they’re doing it because they’re so happy with the new water clarity. There’re big rocks in the pond, but the fishes only flash at the sand surfaces. But I was wrong. The biggest fish dies this morning. Its belly is soft. I didn’t see anything with the scale or in the gill, but I probably don’t know what to look for.

I’m afraid all the big fishes will follow soon. They were acting similarly. The new and smaller fishes are active moving about and still eat. They went through same water transformation, but still eat well and do move about, though not move very much because there’s no stream or undercurrent in the pond.

pH : 7.5
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Could you please look at them and tell me what you think about their health and what I should try. I really hope you could help. Thank you!

Also there was a huuuge rain 10 days ago, first seasonal transition rain, from dry to rainy. It may be relevant?

I’m pumping out 20% water. Test pH at 7.5. Ordering test kit for NH3, NO2, reading a lot and confused more. What should I do next? 🙏
 

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Oh, what a shame that you lost your big koi.
It sounds like an external parasite was introduced with the new fish.
I'm not sure what steps you need to take, sorry.
 
Thanks Naughts for your kind words. Yeah the fish was around with me for 4 yrs. Quite sad and shocked to see it gone. But reading up, i think that my fishes were probably living a stressed life (maybe?) because of their rather inactive and shy from human, so I’m hoping to improve their lives with a bit more knowledge. I’m looking forward to getting a hold of my water test kit.
 
It seems that you have already improved their conditions with the more efficient filter system. Also changing some water after the death will have helped, so long as the water parameters remain stable (pH, GH, temperature).

In a shallow pond the fish will fear predators and also will be subject to bigger temperature fluctuations. Short term you could make 'hides' with plants or rocks to help them feel safe and stay cool. Long term you could look at making the water deeper, and maybe add some water movement. A simple solar fountain will add oxygen.

Photos of the pond and other fish will be useful.
 
Hi, there’s a delay with the delivery of my test kits. I still can’t tell much about water quality yet until tomorrow, i hope. The fishes seem to improve a bit, the bigger ones now eat & move a little bit.

Here’re some pics of them & the pond. The water is indeed shallow. I filled it with sand and made it shallow partly because of my little child’s safety a few years ago. Now the safety concern is gone but I don’t know of an efficient way to remove the sand at the bottom. Haha.
 

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They spend almost all day under the bridge, or in a quiet corner. They are always shy, even during feeding time they don’t like to come near human.

There are many swordtail fishes in the pond. They’d come frenzily for the food pellets and pushing the pellets everywhere. The kois will usually wait for the pellets to come in a distance further away from me to eat. They never need to overcome their shyness.

The younger new kois are picking up this tactic from the old guys and gradually & slowly shying away from human too. :(
 

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Hi Naughts, here’s my water test result:
pH. 7.5
Free NH3: 0.007 mg/l
NO2: 0. mg/l
DO: 4 mg/l
TDS: 130
The dissolved oxygen is too low. My test kit (Sera brand) has 2 reagents. After adding the reagents, the instruction didn’t ask me to wait before comparing with the color. If i wait for a few more minutes the color would darkened further, and DO reading will be about 5-6mg/l. But since it doesn’t ask to wait, the reading is 4mg/l.

I think lack of DO is the main problem. Somehow i need to add some air bubbler system in it and increase the water current inside the pond. But i still can’t explain the flashings.
 
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If there is some sun on the pond could you get hold of a solar fountain? It will break the surface to add oxygen as well as releasing other gases. Something like this:


Flashing is usually because of an irritant, either external parasites or toxins in the water.
Hopefully @Colin_T will comment about the fate of the big koi when he is on. Your big orange fish looks like it has a swelling, and there are possibly some with finrot.

Beautiful set up by the way, I like the umbrella plant too.
 
Thanks Naughts, i’ll look into that.

I just find out that the swordfish population are not healthy now. There’s a breakout of this cloth-like symptom (see pics). I don’t know if it’s a parasite or some kind of fungi. The red ones seems to have more white spots on their body, but i’m less sure about it.
I’m unable to get hold of the kois to check.

Should i add salt to it? I think of 2kg/m3.

What other medication should i use?

TIA

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Gosh, I don't know. Maybe wait for @emeraldking to look, he has good experience with swordtails and keeps fishponds.
 
That's fungus on the swordtail.

A shallow pond will heat up easier during the day than a deeper pond. And when it gets warmer, those koi will become slow. That's normal. They'll rest more and they could seek for more shadow to cool down. That's also normal.
I can't really see anything special on your koi in the first two pics. With the exception of the redness close to the gill (so, not the gill itself) in pic#1.
 
Thanks @emeraldking. Agreed with you on effect caused by the shallow water & heat. Perhaps other factors come to play as well since they also don’t move much in the morning or evening when it’s cooler? Also they have the flashing and the not-eating-well problem lately.

The swordtails are in the same pond. In order to prevent the fungus spreads to the kois, if it hasn’t already done so, i went ahead with a vendor who prescribed this medication.

Tickamit (amatraz 12,5%): dosage 0.2 ml/m3 per day
Roxaci ( Enrofloxacin 10%): dosage 10ml /m3 per day
For 3-4 days, to replace 20-30% water on day 2,3 and 4 before adding medication

I’ve read the labels and these are veterinary medicines for terrestrial animals?! But apparently this vendor seems to be reputable. So i’m on day 2 now. Nothing changes yet for better or worse. I’ll keep everyone posted on the result. Thanks.
 
Hi... i liked to do an update earlier but it wasn't a clear progress so I wasn't sure what to say. We're on day 13 of the treatment now.
The good news is that the kois seem to be reasonably well. They are more active. They eat. They rarely flash. However, the swordfish population is still not doing great. There are still like 5% of them which has that fungus disease and their number reduces visibly. But things seem to be on the right direction, albeit slowly. We administered the above medication for 4 days. Gave further medication of day 8,9, this time includes ivermectin but no amatraz. And further, on day 11,12,13, we gave ivermectin mixed in fish food.

I feel like too much medication already. I think i'll wait a few more days to see if the disease spreads back in the swordfish population or if it continue to slowly disappearing.
 

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