Re: koi pink skin floats upside down plays dead
It's really hard to tell what is wrong with him without the water quality test for NH3/NO2/NO3.
I have no experience in fish sickness after winter as I've never face winter but there's a possibility that during winter, the beneficial bacteria died that cause a spike. It's just my guess.
Worms or parasite could be a problem too.... if you have a quarantine tank, maybe it's good to quarantine and medicate the fish with some general treatments like API general cure.
Keep in mind that if you want to medicate the whole pond, it will cost a lot and it will kill the beneficial bacteria so treating individual might be better if he's the only one with the problem.
Is this fish is eating okay? If it is then you can soak the food in medicated water (mix the treatment in small volume of water then soak the food in it) to feed the fish. It's also a good way for de-worming them.
I'm just asking about the diet because goldfish do not really tolerate a meaty diet. It's good to feed them "meat" like shrimps and worms but the main idea is as supplementary diet for more vitamin like twice a week. They'd do best with veggie based food like spirulina or if you can have algae grow for them to graze is best. Veggetation like water lettuce can also be a healthy food source for them.
Re: Advice for stocking fish and plants in an inherited pond
Hello! I have no idea about local UK fish but I have built a koi pond myself so i can share you some experience about pond building
From what you describe, your filtration system would work fine! But depends on the fish you are going to keep you can set up the filtration with different level of flow
Personally I prefer to let water flowing into filter box using gravity and pump the water back into the main water body because: - With gravity always flowing, even with power out, the filter media is still kept under water therefore crucial bacteria for the system will always survive. - the filtration box will always have the first chamber call... I don't know what it is in english but the idea is that all the big debris will be sink down at the bottom allow only water and very fine debris pass through the filter media so that the system will not be clogged up. Also it will never clog the pump because the idea is only water left at the chamber where the pump will pump water back in the pond. - UV steriliser can be kept in the chamber with the pump, but to maximise effectiveness it can be in the first chamber (however baby fish if somehow sucked up in here may die)
Depends on the water fall, if it is high enough, it will create a good enough flow to flow all the debris into the filtration chamber. However it'd ideal if you can use pips and split the water line into 2 part, 1 for water fall and 1 kept under the water to great flow at the bottom at the pond. Also put valve at these 2 pipes so if needed you can adjust which one will be stronger. (It might also be useful since you have winter in your area :))
One last thing is to make sure you have the means to drain your pond. I recommend you put some kind of drainage in the first chamber of the filter as if you do things right, all the waste would be focused there :)
If you have no idea what am I talking about, i can draw some basic picture to show you the idea :D
Just sharing my koi pond and experience with koi in Vietnam
I'm pretty sure you all agree that Goldfish/koi fish are cold water and yes they can survive cold water.
However they are very adaptive and are being kept with temperature from 25-30C especially in the south of Vietnam.
Vietnam also has a lot of beautiful goldfish but we never did controlled selective breeding for hundred of years like the Japanese to have their luxurious koi.
However for few years back, we started to getting hybrid of selective bred koi from Japan and Vietnamese goldfish. These koi sometimes are as beautiful as the expensive Japanese Koi but much more hardy and adaptive to vietnamese environment. They are called F1 Koi here and are the products of a Vietnamese Fish + Japanese fish.
Then there are Vietnamese Koi which are the offsprings of 2 F1 Koi, these are of course hardier as their genetic are closer to normal goldfish but their color are less beautiful. (Actually they still look good but the patterns is way too random and their reddish color is more orange)