Any koi experts here? Fish gasping for air.

[RichB]

Well technically I know they are gasping because the oxygen level is low and not for air but you know what I mean...

I've been keeping a mixture of pond fish for about 10 years; orfe, tench, shubs, sarasas and koi. Last autumn I built a new, improved pond for them. It is reasonably voluminous being 3 x mtrs wide x 1.5mtrs deep (4') and holds about 6,500 ltrs. For the first time I set-up a pressurised filter with a UV light inside which was matched to the volume of the pond (my old pond had a gravity filter without UV). Since the spring the fish have been perfectly happy and the water has slowly been clearing. Over the last 2 x days the fish have been gasping at the surface in the mornings. Not dramatically but enough for me to wonder what is happening in the water. I have noticed that the clarity has improved this week too, it is almost crystal clear now and I can see the bottom at 4' depth. So I am confused that while the filter and water clarity is improving the fish seem less happy and obviously the water is holding less oxygen. Is there some strange process where algae, being a plant actually puts oxygen in the water? Could it be that the algae was using nutrients and now it's more less gone there is more impurities in the water, even though it is clear? I have lowered the water level by a couple of inches which exposes the return flow pipe from the filter above the surface and this in turn causes aeration. I'm off to the fish shop lunchtime to get some elodea (which the koi will eat!) and have a chat but I wondered if there any fish-keeping experts on here.

I'd be interested in your thoughts.

[crankedup]

You need more oxygenating weed by sounds of it, as you seem to suspect yourself. Also perhaps some mechanical aeration in a section of your tank/pond would help. I'm not a Koi Carp keeper but used to have trouble that you describe with my own pond fish. Came home one summer night to see them struggling with oxygen shortage, filled up the bath and stuck them in that overnight. The next morning returned them to the pond right as rain. Not suggesting this for your Koi though.

[otolith]

A full blown koi pond won't have any oxygenating weed in it, because large koi consider it salad. Even in more natural ponds, it has a more important role in soaking up phosphates and nitrates than in providing oxygen - although photosynthesis will result in raised oxygen levels and lowered CO2 levels (and plant respiration in darkness will do the reverse), the vast majority of oxygen availability is through gas exchange at the surface.

Your koi may be gasping because oxygen levels are low, or because they are having trouble getting what oxygen there is - to rule out the latter, you really need to test your water for ammonia, nitrite and nitrate. It is also feasible that the fish are struggling to breathe not because the water quality is poor or the pond is deoxygenated, but because they have some kind of parasite issue which is affecting their gills. I would say that is the least likely scenario, though.

If oxygen levels are low, it may be because you have too many fish for the area of your pond or because the biological oxygen demand of your pond is too high - the decomposition of uneaten food and fish waste in a biological filter is an oxygen demanding process. Either way, my first step would be to introduce some surface agitation. If you can't do it off the existing pump infrastructure, a small, cheap submersible pump ought to do the trick, set up so that it creates some movement and agitation at the surface.

If your pond is a bit borderline for oxygenation, high water temperatures will cause problems - the solubility of oxygen falls with increasing temperature and decreasing air pressure, so hot, muggy low pressure weather can be particularly problematic.

[RichB]

Thanks all, before leaving for work, as I mentioned, I lowered the water level which causes the water returning to the pond to draw in air. This seems to have cured the immediate problem, fish are all happy. In fact it wasn't the koi gasping as much as the orfe but I know they are more susceptible to this. What puzzled me was the occurrence of the gasping with the clearing of the water. I wondered if there was some connection. More a case of trying to understand what's going on in the water so I can control it. I may cut back slightly on the food and add more koi salad (elodea). As I said though, it's a mixed pond of all sorts, not purely a koi tank, there just happens to be 4 x koi in there.

p.s. How frequently do people wash out the filters? Mine has a reverse flow valve which makes it easy.

[famoussas]

You need an air pump.

Mine did this last summer - as the water heats up it loses oxygen (I think) hence the gasping. Don't put any weed in for koi.

http://www.koi-fish.co.uk/acatalog/Blagden_Koi_Air...

Don't forget you need air stones and piping to connect it all together to.

[otolith]

famoussas said:

You need an air pump.

Or a pumped flow through a venturi.

[RichB]

famoussas said:

You need an air pump. Mine did this last summer - as the water heats up it loses oxygen (I think) hence the gasping. Don't put any weed in for koi.

Thanks, as I said I've sorted the air by having the return flow draw in air ( it's effectivly acting like a venturi). Also as I said it's not a koi pond as such, they just happen to be in there with the other mixed fish. I have hornwort as an oxygenator, koi don't eat it, if you want plants and have koi it's worth trying. I still wonder why it seems to have happened as the water cleared. The weather has been cooler these last few days than most of the preceding month.

[otolith]

Was the pond green? If you've killed off some algae with the UV unit, they're now either decomposing in your filter or have been flushed.

[RichB]

Wasn't ever badly green but the water was greenish over winter and has been steadily clearing during the last 4 x weeks. I did back flush the filter least weekend and a lot smelly green gunk came out.

p.s. Since I started blowing bubbles into the water the hornwort has doubled it's growth rate, it loves it!

[otolith]

Probably also responding to a bit of light now the water has cleared and warmed up!

[fwaggie]

RichB said:

I've been keeping a mixture of pond fish for about 10 years; orfe, tench, shubs, sarasas and koi. Last autumn I built a new, improved pond for them. It is reasonably voluminous being 3 x mtrs wide x 1.5mtrs deep (4') and holds about 6,500 ltrs. For the first time I set-up a pressurised filter with a UV light inside which was matched to the volume of the pond

I have noticed that the clarity has improved this week too, it is almost crystal clear now

Can I ask what pumps, filters and UV you're using?

I've been thinking about rebuilding my small Koi pond, but refuse to do so until I've managed to control the water quality and blanket weed properly.

Currently got an approx 1m x 2.5m x 0.25m>0.5m pond, 15000l/h pump, filter with build in UV that is specced at about 2~3 times the size of my pond, surface skimmer, and still have loads of blanket weed and poor water quality.
(pump, pressure filter and UV are Oase Filtoclear UVA kit)

Also tried the bundles of barley, various chemical things. Nothing works well. One of the chemical things did work reasonably well but I'd need to keep on using it for ever.

I've also drained the pond a few times and pressure washed all the liner to set it up again from scratch.

Only got two Koi in there (approx 9 years old now) who seem happy and put up with the crappy water and weed, but I want it a lot better.

[otolith]

To control blanket weed, you need to remove the phosphate and nitrate from the water that is feeding it. A vegetable filter is the way forward, IMO. You want a shallow pond, maybe only a couple of inches of water on top of several inches of gravel, heavily planted with fast growing reeds and/or watercress. Here's an example:

http://www.pond-life.me.uk/ponds/filtration/vegfil...

[RichB]

fwaggie said:

Currently got an approx 1m x 2.5m x 0.25m>0.5m pond

What's that in feet? Do you mean it's between 9" and 18" deep???