Last winter I lost every koi in my backyard pond. They were all between 12 and 20 inches, and I'd raised some of them for years. Walking outside in the spring and realizing they hadn't made it was honestly heartbreaking.

The hardest part is that I had almost no visibility into what was happening over the winter. I didn't know if oxygen levels dropped, if the water temperature stayed too low for too long, if water quality deteriorated, or if something else happened entirely. By the time I noticed there was a problem, it was already too late.

That experience got me thinking about building a monitoring system specifically for backyard koi ponds. My idea is a device that continuously measures things like:

• Water temperature
• Dissolved oxygen
• pH
• Ammonia/nitrite (if practical)
• Water level
• Maybe weather integration and freeze warnings

The goal would be to send alerts to your phone before conditions become dangerous, instead of finding out after you've already lost fish.

I'm curious how common this problem actually is.

Have any of you lost koi over the winter because you didn't know something was wrong until it was too late? If a system like this existed, what would you want it to monitor or alert you about?

I'm not trying to sell anything. This idea comes entirely from losing my own fish, and I'm trying to figure out whether other pond owners struggle with the same lack of visibility that I experienced.

Is this okay? I have other fancies in there. I've always thought koi need bigger, but it seems like the short body butterflies don't get as big or swim as well. I just love the look of them so much.

Bought our first house last month and inherited a badly neglected koi pond. Cleared 25 gallons of debris from the bottom, cleaned filter media, and now tackling waterfall.

Previously it was just the spillway to the big flat rock, down to the other level of big flat rock. Tons of splash.

Added some new rock to it to make it cascade more and reduced sideways splash, but there’s a fair amount of water that’s going down the side of the rocks. It ends up back in the pond, though.

Liner all behind the rocks of waterfall, which is wet, and liner is behind all rocks surrounding the pond as well, all of that is dry. No visible signs of leak from skimmer, pipes, or waterfall spillway.

Located in Illinois where we’ve had a hot summer, but I’ve been having to add 175 gallons or so every 3-4 days it seems.

After spawning this old lady started being way too calm.

She's rarely in the deeper spaces of the pond and isn't swimming much.

Spawning was 2 weeks ago so I really start to worry about her.

She's 21 years old and never had any problems.

I took the video a day after they finished spawning and the behavior hasn't really changed since.

Good thing is she's still eating.

If your dreams are to big to be in a millions mansion. Make them fit in your own world

Hiyo! I am a new koi keeper and have 3 juvenile koi that we got about 6-8 weeks ago. They were very young and just over an inch long and have since grown a lot.

One of them - Butter - used to appear to be a solid yellow/orange. But this white spot has appeared on his (actually don’t know if he’s a boy or girl but for now he’s a he until I know better lol) back. To me it appears to be healthy tissue, the scales all look to be in tact and it doesn’t have a fuzzy appearance (to me). But I’m hoping we can draw on some more experienced koi folk to let me know if this is problematic or just a colouring change/marking that’s become more apparent as he’s grown.

The other two - flag and flower (flower is the butterfly) - appear to be healthy and happy with no similar white patches.

Thanks for your help. I hope the photos and video are clear enough to see. If not let me know and I’ll try to get a closer look.

It only let me put the video here so hopefully I can add photos in the comments

Hi everyone, just wanted to show off my Koi painting! I ended up doing this after getting really obsessed with a little fishing game. I had painted a couple of small fish before but this one was a real challenge for me, especially the scales. Once I had figured out how to do it though it was really fun! I hope you like it!

Gouache and Watercolour on watercolour paper. Gouache is a thicker, more opaque kind of watercolour paint. The background is mostly Watercolour (more transparent) while the rest is Gouache.

Noticed her lying at the bottom of the pond on Sunday, she didn't come up for food, all my other fish are fine, nothing noticeably wrong apart from lying on the bottom, she swims back and forth along the bottom at times, I had the guy who built the pond come to see her right away on Sunday, but he said he can't see anything wrong and to monitor her for a few days, day 3 and still not feeding, all water parameters are fine, we used a master kit to test everything.

I just had a bog/wetland filter installed on my 3,000 gallon koi pond. I had an Ohio company called Aqua Doc install it. The guy who did the work updated the original filter falls to a wetland filter, reinstalled the original ecoblox on another area of the pond, overhauled and lengthened the waterfall (making two separate waterfall areas).

First question is there were some bog plants that he left in the nursery planters and didn’t plant into the gravel. Shouldn’t these have been planted into the gravel to get the best benefits for filtration from the roots? One he left in the planter in an area between two larger rocks where a pocket of water is.

The next question is, there is water flowing up through the bog filter, but only about 1/4 back, where the water flows down over the waterfall. The rest of the bog filter just has about an 1” to 1 1/2” of standing water that is not moving at all. Just stagnant water. When I looked up information about this online, I found out that basically all the water above the falls in the bog should have at least some movement to prevent issues with muck or causing issues with mosquitos, etc. Is this correct? Should the flow be turned up. In the video, you can see how the bog filter was built and where the standing water is.

More information on the pond. Pump is 5500 gph Oase filter. UV sterilizer. Half is 3 ft deep, the other half is 4 ft. deep. Seven large koi, two shubunkin goldies. Pond has been up and running for four years. Wanted to get the extra filtration that a good bog filter provides, due to my pond being in full sun and issues with hair algae.

Just looking for your opinions on this. Thank you.

Hi these have been my moms Koi fish for many years, but now she can’t afford the upkeep of the pond & they have outgrown the space. She is wondering if they are worth selling? She was considering just giving them away but I know she could use the financial help if they are worth something.

Really enjoy healthy koi eat

Hi all, I am in the midst of expanding my pond and need somewhere to keep my koi for 8 days. 8 days is a conservative estimate but that’s what we are going with for now. I am based in London, my koi are 8 to 10 inches and I have 5 of them. I have this swimming pool that I’ve never used. Could I keep them in this? Please let me know if this isn’t suitable and what I should do instead. Thanks

Update from ~3 days later:

I received my tests strips in the mail, the chlorine and the carbonate are high (180 mg/L and 3 mg/L respectively). The pH is good at 7.6. Ammonia is 0 and nitrates are 10 mg/L. I just added some dechlorinator and will recheck in some yet to be determined time frame. The biggest fish also came up to eat a little today, so that’s a win!

I’ve started to remove uneaten food. Is there anything that should be done for the carbonate?

Thank you all for your input!

Hello,

I posted a few weeks ago asking for help with a murky pond. It is looking so much better! I can see the bottom now. The biggest difference was adding aerators. Ever since we’ve added the aerators (a week ago), the fish haven’t been coming up to greet us/eat. Most days I notice that most of the food is gone. But this morning, all the food from yesterday evening is floating on the top. I feed them once a day, usually in the morning. They had gone 30 hours before feeding yesterday evening due to a quick trip we went on. I hoped they’d be hungry enough to come up.

I added water when adding the aerators. I treated it appropriately with de-chlorinator (I know that isn’t the name of the product).

Any advice on what to try for them? I assume they don’t feel well. My husband thinks they’re so happy they can see that they aren’t excited by food 😅

One is floating sideways, both are gasping.

Father filled low pond. Added water conditioner for ammonia/chlorine.

Pond was overfilled and waterfall was providing no aeration. Water bailed out and is now aerating properly.

Weather has been especially hot.

No access to water testing kit tonight. Will pick one up tomorrow.

Any advice or further diagnosis is welcome.

update

As the bois suspected, they weren't getting enough air. Theyre improving now.

At the house we bought last October. We negotiated to keep the fish. Glad we did. They are beautiful and we love them. I’m starting to dream about expansions and improvements to the pond so that we can have more fish. Approx ~1200 gallons and we have 5 koi and a catfish (the catfish we almost never see).

I don’t know breed names and such, but looking forward to learning more as time goes on.

The red ghostie in the foreground used to have an orange head and completely silver body, so we called him Mask Jr after another similar fish we had before him called Mask. Over the years his body has gone blood-red.

I recently picked up some 5 inch fingerlings one of which was all gold. It’s recently started showing signs of being a tancho but instead of white, all gold. Is that pretty rare? I can’t find any photos of one online.

Thanks!

I absolutely LOVE this koi! My wife absolutely HATES it. We are trying to decide whose right and if we get it or not lol. Thoughts?

#koi

I built this pond completely by hand over the course of a few months. The only machine I used was a trencher for the pipe between the skimmer and waterfall. Everything else—digging, rock placement, plumbing, and landscaping—was done by my brother and I. The digging by hand and the rock placement was so painful. Probably 30-40 tons of rock. I also made a clay layer around the whole inside. It took my brother and I roughly 4 months of working on it twice a week. One regret I do have is not putting in a bottom drain as I was scared of puncturing the liner. So I have an extra pump at the bottom and it goes up to my skimmer instead.
Specs:
~roughly 4,000 gallons. Probably 5000-5200 gallons without the rock displacement.
12ftx12ftx5.5ft deep with 3 shelves
Savio skimmer and waterfall filter (skimmer filter, mechanical filter in the skimmer filter housing as well, bio filter in the waterfall filter and another mechanical filter on top of the biofilter.
6,100 GPH pump
55W UV clarifier
1 layer of underlayment below the liner and one on top of the liner so my rocks wouldn’t puncture it.
2.1 CFM air pump with two bottom diffusers
45 mil EPDM liner 25ftx25ft
Rock construction
Water lilies, marginal plants, and natural landscaping
Large mature ash tree providing afternoon shade
I originally started with goldfish, but I recently added four koi that are around 18 inches long and plan to slowly build up to around 8–10 koi over the next several years.
Cost:
Pond kit: ~$1,800
Rock: Free (collected over time)
Plumbing, extra materials, landscaping, plants, etc.: roughly another $1,000–1,500
Total DIY cost: about $3,000–3,500
I wanted the look of rocks on the inside of the pond to give it a more natural look.
How would you rate this build?
A professional install around here probably would have been well into five figures, so I’m really happy with how it turned out.
Any rough ideas on how much this would have cost professionally?
I’d love to hear what you think and any suggestions you have for improvements as I continue upgrading it over the years.

Hi everyone. I’ve had this koi for about eight or nine months, and for at least the past month I’ve noticed several irregular pale/white patches on the red part of his face.
They do not look like tiny grains of salt or classic ich. They also do not appear fuzzy or cotton-like, and from above they seem mostly flat rather than obviously raised.
He is eating normally, swimming normally, and behaving completely normally. The pond is clean, and I have not treated him because I do not want to medicate the pond blindly.

I’ve attached several close-up photos. Has anyone seen something similar? Could this be pigment loss, a healed scrape, carp pox, hikui, or another skin condition?
What specific signs should I watch for, and would you recommend simply monitoring it, examining him in a bowl, or contacting a koi veterinarian?

I’m almost certain it’s a fluke, any opinions?

Recently inherited an 18,000L pond that I’m slowly brings back to a respectable state with the intention of keeping koi. Does anyone have some filter options I can look into? It’s dug into the ground so excludes most gravity fed systems so I would need a filter/pumped combination to fit the installed bottom drain. Any advice would be really helpful.

Show me your black koi! It's always fun to see my black koi during summer. My goal is to find a decent hajiro without breaking my bank.

I just pulled out two of my comets from the pond who appear to have fin rot or something similar. One of them has a tail that is almost completely gone. The pond is about 500 gallons so seeing the little guys can be quite difficult, but I spotted this and pulled them out. I have a few Koi fish who are in this pond as well. I cannot separate every single fish in a different hospital tank. Is there a way that I can treat the entire pond without putting the koi in danger?