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| We offer a Koi Rescue Service. |
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I would like to start with a short presentation to give us all some background on aspects of handling koi in hot weather and then we’ll open this us for general discussion and a Q&A session. If you wander around on the koi chat sites online you find that the concern about how to deal with koi in the winter starts up in September. However, here in Florida winter is our easy season. Aside from Spring, the touchiest time in the koi pond is, Summer. Summer means heat, for us and for pond water. Though water has a substantial thermal inertia by late May or mid-June the water temperature is pretty warm. My own pond, before it was shaded, water temperature hover between 85F and 90F all summer. The shallower your water the higher its temperature can climb which implies that proper pond design can have an effect of the problems of summer. Other things that we have to watch are: ammonia levels, they are more toxic as water warms; water carries less O2 in summer; fish metabolism is increased in summer meaning higher O2 demand; bacterial respiration doubles with each ten degree rise in temperature which also puts higher demands on oxygen; pH levels are effected by all summer stress factors. In view of these potential problems almost any minor disaster can trigger a major pond emergency. One of the best ways to reduce the effects of summer on your fish is to cover your pond. In preparation for this report I took the temperature of my main pond and the temperature of a small quarantine pond near by. My pond is covered by a pergola of thick vining plants and the tank is open to the sun. In the hottest part of the day the main pond was 8F cooler than the quarantine tank. 8F is a change of about .8 mg/L in Dissolved Oxygen, (DO) which we will see is a great amount. In addition to keeping the sun off your pond and in-ground pond may be cooler due simply to the heat sinking effect of the ground. Greater depth also plays a part in keeping our fish comfortable as does more volume. These are things to think about if you are building a pond, but what do you do with what you already have? First and foremost is aeration, aeration, aeration is the key. You have heard me say before that there are two things you cannot do; one is filter too much and the other is aerate too much. This goes triple in the dog days. It is now time for us to shift over to a discussion of Dissolved Oxygen, because in the end DO is the 800 lbs. gorilla of summer pond problems. Please do not feel insulted, but I feel it important to point out that fish do not "breath" water. They process water over their gills where free oxygen dissolved is removed and enters their blood stream. So the amount of DO in the water directly effects the immediate welfare of the fish. Oxygen gets into the water in several ways. If you run plants in your pond or have any type of algae including green water and string algae than a by product of the plant’s daytime respiration is gaseous O2. However, the reverse happens at night and the plants take O2 out of the water at night. This the reason the lowest DO levels occur just before dawn. Even without any vegetation O2 infuses at the air-water boundary. In short at the surface of your pond. This happens all the time, even in still water. But, even a light wind can cause ripples that may effectively increase the pond’s surface area by 2 or 3 times and the more surface area you have the more O2 you transfer. When we aerate it is the air-water boundary that we manipulate. I’m going to get a little technical here, so bare with me. One Liter of pure water at 0C is said to be saturated (normal DO level) when it contains 14.6 mg of O2. This is about as good as it gets in the DO world as there is an inverse relationship between water temperature and DO levels. The hotter the water the less DO it can contain. At 25C (77F) the DO saturation drops to 8.2 mg/L, and at 92F it is half of what it held at its best or 7.3 mg/l. This is the reason that we never worry about DO levels in the Fall, Winter and Spring. The water is cool and holds plenty of O2. Interestingly, altitude and atmospheric pressure have little effect on the oxygenation process so, we gain no advantage living so near sea-level. Please note that these numbers are for pure water. If the water contains other chemicals, suspended particles, algae, and other things as our water does, its DO capacity is lowered. This means salt water holds less O2, so you may not want to run high salt levels in Summer. Given that our fish need good DO levels, what happens when the DO level drops lower and lower. According to the water quality criteria for the Commonwealth of Kentucky, DO levels of 5.0 mg/L and lower cause extreme stress to all aerobic life. This includes not only the fish, but other organisms in the pond such as aerobic bacteria. As it is these bacteria that make your bio-filter work, lower DO levels can damage your filter. At 1-2 mg/L larger fish will die in a few hours. Many of us have horror stories about losing fish from anoxia. Mine goes like this. When Sandee and were fish vendors we had 30 koi of 8 to 12 inches that had survived three or four cullings and were ready for the fall show. We had them in an 800 gal. pond with an adequate pump and filter. However the surface of the pond was covered with hyacinths. One night the hose slipped of the pump. Between the lack of moving water and the plants sucking all the O2 out over night, we lost 20 of the 30 fish by the next morning. Only the smallest fish survived. Now you know what damage low DO can cause, it is important to be able to recognize it in your own pond. The tell tale signs are: 1) Fish will be swimming near the surface, gulping air. 2) Large fish will be in greater distress than smaller ones. 3) These behaviors are more pronounced in the morning. 4) The water may turn dark in color; gray to black or brown as algae die. 5) As the pond dies, it may give off a foul smell. 6) Remember this can happen in a matter of hours. So how do you react to this emergency? 1) The first thing to do is get the water moving however you can. Air pump driven air stones, set up a water pump so it will"fountain" or spray water about the pond, 2) If your water volume is small you may want to change some of it, provided you can replace it with good oxygenated make-up water. This will also help lower the water temperature and increase its O2 saturation level. Please remember that water from a hose or from a well has very low DO and if not handled property will exacerbate your problem. 3) Introduce hydrogen peroxide 3% USP (standard drugstore type) @ 1C per 100 gal. as a maximum dose. Start with 1C per 500 gal. at first. 4) Remove as much debris, old food and mulm as you can, this includes dead fish. 5) Clean your filter to make sure it is free from organic matter and allowing maximum water flow. Make sure the water return is as agitated as it can be. Telling you what to do when you are in an emergency is fine, but it is better to tell you how to stay out of a low DO condition altogether. 1) Make sure you agitate your water as much as you can. a) Have a water fall. B) Run an axillary air pump and air stones: Air stones work by causing a surface disruption at the air-water boundary. They do not aerate the water by themselves. 2) Keep plants, but keep them to a minimum. Floating plants such as hyacinths should not cover more than one third of the surface at any time. Run anacharis and other plants considered oxygenators, but keep them under control. Remember they take out O2 at night. 3) Keep your filter clean and free running. 4) Make sure your pump pickup is at the far end of your pond from where the water returns. This assures good water flow throughout the pond. Your pickup should be a bottom drain or from a sump at the lowest part of your pond. 5) Cover your pond to keep the water cooler in summer. 6) Always spray makeup water into the pond. 7) Get a UV filter to keep the greenwater down |
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