Goldfish developed white patches

[Yvonukon]

Hi all. We have a very small pond, about 230 litres with a filter and air pump. We have 3 long tailed goldfish and two butterfly koi, bought at the same time, about May time this year. They have been fine so far, eating well and swimming fine, energetic etc. But in the last couple of days I have noticed that one of the gold fish has white patched around its head, patches not spots, and a bit of whitening along the top fin line. He seems fine apart from that regarding his behaviour etc.

I have tested the water and most parameters are ok besides low in chloride and total chloride, but very low on the scale for salinity and high on cyanurique acid (its written in french and dutch but I guess you experts will know what this is).

Last year we lost our fish to slime disease, only had 2 fish then and ive since treated the water for KH and with good bacteria and pond salt. when the tests were ok we added these fish from a reputable source. Could it be the slime disease coming back? I hope not. The weather has been very hot here, about 28 -33 C and I have shaded the pond. (it is above ground).

I attached some pictures. Any advice for me please?

 

[Yvonukon]

Bumping: Is this just a normal thing?

 

[WaterGardener]

This photo looks as though scales are missing. That can be caused from a fish rubbing on something or toxic water conditions like high ammonia levels.

Are your water tests for pools and not ponds? You need liquid type tests for ammonia, nitrite, nitrate, pH and KH. Please test the water for those things and post the results here.

What do you mean by treating for KH?

Your pond is much too small for the type and number of fish you have. Koi need at least 500 gallons of water per fish. Goldfish should have 50 gallons per fish, but with a lot of extra filtration you could possibly get away with 20 gallons for each.

Please re-home the koi. They grow very quickly and produce a great deal of waste. They can grow to over 30" long and are very stout fish. Your pond simply doesn't have enough room for them.

What type and how much filtration does your pond have?

Sorry for all the questions,but we need more information to be able to help you and your fish.