Koi shedding scales

[Bobo8]

Hey guys.
So I take care of some tanks for a business downtown. Anyway one of the tanks has 3 koi and one of them has been losing some scales. First thing the tank is too small but I am doing the best I can for these guys. Anyway for some reason they also have 2 huge silver dollars in there so the temp is around 25 I know that's too hot for koi. But these fish have been there for years and I just noticed scale shedding in the past month. I have only been working with them for a few months. Anyway parameters are
ammonia 0
Nitrite 0
Nitrate never higher than 40
The tank is a 280
Temp around 25
Filtration they have an fx5 and an fx6
Let me know if you need more info!
Here is a pic of the koi whose losing scales.

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[Bobo8]

Oh I forgot to mention the koi will be moving to a 3000 gallon pond in summer.

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[Delapool]

Are the scales looking ruffled or lifting at all that might mean a bacterial infection? Any flashing?

Other one could be to check is if feed is still good and fresh.

 

[Bobo8]

Nope they are flat when they come off. And feed is in an air tight container.

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[Delapool]

Feed was one I was told to check for this but it was a long time ago so maybe it was a guess on their part.

Well, I'm pretty much out

I'm assuming that things like water company changing tap water chemistry,

ammonia and then scale colour change / loss several days later,

office chemical sprays,

ph in range for tank and hasn't changed for tap water (same for kh),

another fish attacking it.

These have all been crossed off?

 

[Bobo8]

Hmm well one thing could be the tap water. They will not let me use ANY chemicals in the water. Not even water conditioner. Now I have only been there for a few months and I make sure to do a weekly water change so I don't know what the person before me was doing but it could be the increased chlorine content? I mean they have been this way since forever and the koi are at least 10 years old not that I'm saying it's okay not to use it!!

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[Delapool]

Hmm well one thing could be the tap water. They will not let me use ANY chemicals in the water. Not even water conditioner. Now I have only been there for a few months and I make sure to do a weekly water change so I don't know what the person before me was doing but it could be the increased chlorine content? I mean they have been this way since forever and the koi are at least 10 years old not that I'm saying it's okay not to use it!!

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Wow, bit surprising of them I guess.

I have seen numerous threads on tap water changing chemistry and causing issues but never kept track if certain times of year.

In summer here I can pick a change with kh reducing mainly. Ph drops a little but kh can halve and as we have soft water already I have to keep an eye on it.

Maybe a pool test kit for chlorine or an aquarium one?

Might be worth asking what the previous person did on water change routine maybe? Just to see if he did it less often which I'm wondering if actually helped them.

Must confess I'd be tempted on a pinch of seachem safe just in case but oh well.

 

[Bobo8]

Oh trust me I want to but then there's the issue if I'm using it all the time and rhen I quit the next person doesn't use then there might be problems! I tested the chlorine and it is in the caution section. So not through best but not the worst.. but I know the last lady and when I tested the water when I came in the nitrates were like 300+ so no way that was helping hahah

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[Delapool]

Sounds like you would be doing more water changes then the previous person? That might fit as well if this is the problem. Ideas anyways.

Do the filters run carbon at all? Our house tap filter is mainly carbon and will take out the chlorine. (Actually now I'm wondering how it would go running a carbon filter at end of hose when filling tank. I might see if I can test ours this weekend as we have a chlorine test kit).

https://en.m.wikipedia.org/wiki/Carbon_filtering