Water Gardening Direct Blog

How to Solve and Avoid Low Oxygen Problems

With the warm weather we have all been waiting for finally on its way you may need to make sure fish enjoy it as much as you do. As temperatures start to increase, the ecology of a pond will change. Increased temperatures will increase the activity of your fish and hence the consumption of Oxygen, whilst at the same time the rise in water temperature reduces it’s ability to carry oxygen, these factors in severe cases can be fatal to your fish.

For plants, fish, amphibians, wildlife and even many forms of bacteria, an environment which is rich in oxygen is critical. Although oxygen is present in water and the air around us, ensuring a sufficient quantity of oxygen within a pond is not something that should be left to chance

What happens in natural ponds, why don’t they need any help?

In most wild ponds, nature has a very brutal way of establishing a balance. They normally have much smaller quantity of fish per 1000 gallons of water than there would be within a garden pond, allowing waste products from the fish to be diluted without causing them harm. Because of this low population, there is normally plenty of oxygen for the fish population. However in natural ponds sometimes things go wrong. If a very fast growing pond plant overtakes the pond (such as parrot’s feather or even blanket weed), or if the fish population suddenly explodes. It can cause a massive reduction of oxygen during hot humid summer nights and in extreme cases, kills most of the fish population (usually killing the largest fish first).

Why do some plants have this effect, I thought they were Pond Oxygenators?

Although plants don’t breath in the same way we do, the cells within plants continually use oxygen to help fuel growth and repair (this is called cellular respiration). This process happens 24 hours a day and carbon dioxide is given of as a by-product. Fortunately, during daylight hours another process called photosynthesis more than corrects the balance by producing oxygen as a by-product of absorbing energy from sunlight. So although plants can boost oxygen during the day, they do not at night and in fact are one of the oxygen consumers.

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Can I add additional Oxygen to my pond?

In garden fish ponds the balance between fish and plants is more commonly in favour of the fish, with plants often as decoration only. This is where nature needs a helping hand to keep the oxygen levels up. In addition to plants Oxygen is added to the water wherever water comes into contact with air, so the greatest quantity of Oxygen enters your pond at the surface, so ensuring a good circulation of the pond is the first step to keeping Oxygen levels up. Your pump should be at the bottom of the pond, where the oxygen content is lowest and should push water up to the surface and ideally spread it out across the surface of the pond. Adding a fountain or waterfall all increase contact time between the water and air and give more opportunity for the vital Oxygen to be absorbed.

For more information on these products, click the following links

Blanket Weed Treatments : Filter Kits : Pond Fountain Pumps : Pond Spitters

There are also other ways to put water in contact with air. Pond air pumps can be a fantastic way to improve the oxygen levels within a pond. Although each individual bubble may be tiny, releasing millions of bubbles into the bottom of a pond with an air pump and air stones, keeps the air in contact with the water as the bubbles rise to the pond surface. In addition to the direct transfer of oxygen achieved by this process, an added benefit is that the rising bubbles will drag de-oxygenated water from the base of the pond back to the surface for re-oxygenation. The Oase OxyTex CWS air stone is particularly good at releasing thousand of very fine air bulbs and also acts as a boost to your filter system.

For more information on these products, click the following links

Pond Air Pumps : Air Pump Accessories

The time of lowest Oxygen levels are normally at dawn and often the most common sign of an Oxygen problem is when the fish are up at the surface first thing in the morning with their gills moving quickly. If you see this then you need to act quickly as your fish maybe in danger and sadly it’s always the largest fish which die first. A very useful fast acting treatment is Oase’s AquaActive Oxy Plus, which actively releases Oxygen quickly straight in to the water because it is a hydrogen peroxide granulate fixed on a carbonate. When it becomes wet the carbonate goes into solution and the peroxide starts to react with the water. The result is pure oxygen and water. Due to the fact that the carbonate goes into solution very slowly we have a immediate but long lasting effect. This treatment can be added to your pond before a problem exists and will spring in to action as and when needed.

For more information on this product, click the following link: Oase OXY Plus

You can never have too much oxygen in a pond and many experts believe fish are healthier in environments which are rich in oxygen, and they would recommend adding air pumps to almost all fish ponds as a matter of course not just when and if the Oxygen levels are dangerous.

The simple rules to follow are:

A) DO NOT over stock your pond. As a rule of thumb a pond should be stocked with no more than 100” of fish (excluding their tails) per 1000 gallons of water (5.5cm per 100L). If you exceed this limit you should be very careful to ensure the level of oxygen in your pond does not fall too low (particularly at night) and be carefully of fish fry which as they grow will greatly add to the oxygen consumption.

B) DO NOT allow oxygenating plants, blanketweed or green water to overtake your pond. Remember that although in the day plants produce more oxygen than they use, at night they don’t produce oxygen at all, but they do produce a lot of carbon dioxide.

Garden Pond Protein Froth and Foam

Protein Froth is an unsightly foam which sits on the water surface and can look like some one has tipped washing up liquid in to your pond. Protein Foam is normally formed where the water comes back in to the pond at waterfalls and filter returns, but can also happen around fountains and venturi’s. In most cases it is caused by Protein, which is an oil based chemical that floats on the surface of the pond and makes the bulbs last longer. This oil is a natural chemical and will eventually disperse by itself, the problem is it will take months to do so and your pond can look awful until it goes. Not only is it ugly, but it can be dangerous to fish as well. The surface of the pond is where most of the essential gas exchange takes place, allowing Carbon Dioxide out and Oxygen in to the water, if the surface is then coated in protein oil it can hinder or even stop the gas exchange. So solving this problem not only to improve the appearance of your pond, but also ensures the health of your fish. Thankfully this is one of the simplest things to eradicate in your pond, TAP Anti Foam will literally make it disappear in front of your eyes.

Click here to go to our TAP Anti Foam Treatment Page

TAP Anti Foam is designed to breakdown the froth in garden ponds, created by the excessive build up of protein in the pond water. TAP Anti Foam is non toxic, harmless to plants, all fish and other aquatic life and does not affect bacterial filters.

Where did it come from?

It helps to understand why it has occurred in the first place, because in some cases it is preventable. The two most common causes for Protein Froth are spawning from fish/ frogs/toads and feeding the wrong type or quantity of food. Spawning is not something you have control over, but you can control the amount and kind of food you feed. If the fish are fed too much in one go, they will wolf it all down, but it will pass through them quickly and much of it comes out as waste including Protein. In the summer month’s food should not last for more than 5 minutes, any more and you will be overfeeding. If you are not convinced that the fish will get enough food this way stick to the 5 minute rule but feed them several times a day. To help you keep an eye on how much food the fish receive you can use a floating feeding ring, these float on the surface of the pond and keep the food in one place. In the cooler Spring/Autumn weather, fish are programmed not to absorb Protein, so feeding them a growth or high protein food at these times of year will mean it passes straight through them and comes out in to the water. Use the low protein wheatgerm foods at these times of year.

So the best way to prevent the protein foam from occurring is to feed your fish the correct kind of food for the time of year (and temperature) and to feed little and often.

How And When To Feed Your Fish

Fish have evolved over the years to extract the appropriate nutrition from the food they eat. Commercial foods have been designed to offer what they need when they need it. During the cooler temperatures fish do not absorb as much Protein, so Wheatgerm Fish Food has been developed to meet these demands, it is low in Protein, but higher in other nutrients. In the warm summer months, fish want to take on as much protein as they can, either for body growth or to help create eggs and so Growth Foods are available which are high in Protein. The table below offers a guide to which food type is best for the time of year or temperature. Knowing how and when to feed your fish is both good for your fish and your pocket.

Summer Feeding

During the Summer months your fish can seem to be ravenous and feeding them multiple handfuls of food, which they wolf down is very tempting, but this is not necessarily a good thing for them, the pond or your wallet. If you feed the fish a lot in one go, they will get full and the food will pass through their body quickly leading to much of the food coming out as waste. This will pollute the pond leading to foaming (protein froth), filters which need cleaning more frequently, added nutrients for algae and over weight lazy fish.  In the wild your pond fish would naturally look for food all the time and would eat little and often, so this is what we should try to help them do.  Feeding small quantities of food which can be consumed in 5 minutes only is ideal, this can be done as often as your lifestyle allows, but if you want to promote growth the more frequent the better.  By feeding in this way, not only do you ensure that most of the goodness of the food is used, but also it keeps the fish slightly hungry and they will explore round the pond looking for more food, this is good for muscle growth and general health.  You will also probably spend less on food.

Using the little and often option for feeding will soon lead to your fish coming to you when you approach the pond.  This is ideal, it allows you to appreciate them better, to visually inspect them to ensure they are all healthy and can be the beginning of being able to hand feed them.

One of the problems with feeding fish in a well planted pond is that the food can float off in to the marginal plants making it hard to know if it has been eaten or is just rotting away.  This can be avoided by using a feeding ring, this is a very simple floating ring which keeps the food in one place, so that you know what is being consumed.

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Keeping an eye on things

One food to stay away from, or at least be very careful of, is flake food.  Around 50% of flake food sinks, which is fine in aquariums, but in ponds it can mean that you do not know how much is being eaten and can lead to a rotting pile at the bottom of the pond.

In short the best thing for your fish is to feed them the correct kind of food for the temperature/season and do this little and often.

Green Water Problem – Dont let it spoil your pond

As the sun comes out so can the algae which causes green water. This algae is a microscopic single celled plant which is so small it passes through most foam and filter material. In the height of the summer, provided it has sunlight and nutrients, it can reproduce at a fantastic rate, clouding a pond completely in days. It is normally more of a problem in fish ponds, because the fish waste (Ammonia/Nitrate) is being continuously converted by the filter in to plant nutrients (Nitrates). However, in addition to being unattractive it can also cause problems in the pond affecting the pH of the water and the oxygen content.

Even though green water algae is small, like all plants it photosynthesise, this process in underwater plants gradually pushes up the pH of the pond which accelerates algae growth and if left to get very high can seriously affect the fishes health. The process of photosynthesis produces oxygen during the day, but at night the process is reversed, so a pond full of green water may suffer from lack of oxygen at night, which can be a real threat to any fish.

So how can you solve the problem?

In Filtered Ponds

In most ponds, a correctly sized filter system, which is installed and maintained correctly, should easily deal with green water. Some of the common mistakes which can affect the performance of a filter system, are poor flowrates, poor flow patterns, old UV bulbs and poor maintenance.

For a filter system to have a chance of winning the battle in your pond, it has to beat the growth rate of algae and in the summer this is very fast. As a guide the whole pond volume needs to be circulated through the filter once every 1½ to 2 hours. So a pond of 4500 litres (1000 gallons) needs a flow through the filter of 2250 – 3000 litre per hour (500 – 667 gallons per hour). Pumping water through hose, a UV, filter and maybe uphill will all slow the pump down and this needs to be allowed for when sizing a pump for filtration, so that the correct flow can be achieved at the end. If you have clarity problems try testing your flowrate. This is easier with 2 people, one with a stopwatch, the other with a bucket of a know volume. Simple time how long it takes to fill the bucket from the outlet of the filter, then divide 3600 by the time (in seconds) to fill the bucket and multiply by the volume of the bucket. The result is the flowrate.

As mentioned ALL of the pond water has to pass through the filter system every 1½ – 2 hours, if your pond pump is in the wrong place you maybe circulating one end of your pond really well, but allowing the other end to pollute the rest of the pond. This can lead to a filter which is doing all it can to keep up, but a pond that can produce as much algae as it likes. Avoid locating the pump right underneath the outlet from a filter or even half way down the pond. Ideally the pump and filter return need to be at opposite ends of the pond to one another creating full circulation. To improve collection of particles it also helps if the pump is on the base of the pond, at the deepest point.

Old UV bulbs are very common cause of green water. The bulbs are not especially cheap so everyone try’s to get the most out of them. But every UV bulb gradually loose power from the moment you put them on and so become ineffective within a set time scale. UV bulbs should be replaced every 6 months for the double ended fluorescent style or every 12 months for the low wattage PLS or PLL bulbs. The blue glow you see from the bulb is not UV light, our eyes can not see the UV rays emitted and as such the blue is just and indicator that the bulb is on, not a measure of whether it is still giving out UV light. To help with the price of bulbs we offer a buy any 3 replacement UV Bulbs and get the cheapest 1 free.

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Clean UV’s. Most UV bulbs are protected from contact with water by a Quartz Sleeve, this quartz sleeve can become coated with limescale, just like your kettle. But the limescale will hugely impact on how well UV light will travel through the quartz and needs to be cleaned off. If this is done regularly then removing the quartz sleeve should be easy and you can use clear vinegar or lemon juice to soak in to the limescale and gently rub it off. If the UV has not been cleaned regularly then I would not try to remove it, but instead clean it inside the water chamber. This will involve filling the chamber with kettle descaler or equivalent and letting that loosen off the limescale, but you MUST thoroughly clean this chemical out before reconnecting your UV.

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The last stage of the system is the filter medium. In most cases it is the foam that catches the green water particles, and it is vital that the water has to flow through this foam for it to be effective. If the water can find a way around the foam then it will and so will the waste, so make sure the foam is in good condition and a snug fit in the chamber it is in. The other issue with filters is cleaning, you maybe cleaning it too often or not enough. Although the foam is designed to catch algae, the particles are very small and despite being flocculated (clumped together) by the UV, they are still not much bigger than pinheads. New or very clean foam struggles to catch these particles and it is only as the foam gets dirtier and the holes and pathways begin to block will the algae get caught, so if the foam is not dirty do not clean in it. At the other end of the scale if the foam is too dirty water may be able to find away around it, either because the filter has a built in bypass or the foam is distorted with the amount of waste.

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If you want to try to boost the system and get a quick result then Interpet’s Green Away is a very good treatment. It does the same job as the UV clumping the algae together so it can be caught, but one treatment can make sure the whole pond has been dealt with.

Click Here to go to our Interpet Greenaway page

In unfiltered ponds

If the pond is not filtered then you are relying on natural competition from other plants to beat the growth of algae and it can be very difficult to hit the right balance. For the first couple of years of a pond life the algae will probably win the battle, but as all your plants mature they will create more shade and use up more nutrients and hopefully tip the balance in your favour. The plants which will have the fastest impact are shade producing plants like lilies and duckweed along with fast growing oxygenators. If you can create 60-70% surface cover then algae both green water and blanketweed should struggle. Lilies can take several years to become big enough to create this amount of shade and the fast reproducing duckweed can fill the gap very effectively, but a word of warning, duckweed is virtually impossible to eradicate, so you may just be swapping one problem for another. Virtually all oxygenating plants are fast growing and so consume large quantities of the nitrates and phosphates required by the algae to grow. More long-term areas of Reed’s and Iris’s are excellent at extracting the nutrients and as such they are a good idea to include in your planting scheme. If you can not wait for the plants to mature and want to give them a helping hand then the Oase Aqua Active Pond Clear and the TAP No More Greenwater are both very effective but gentle treatments.

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Other Useful Links

Click Here to go to our Pond Volume Calculator page

Click Here to go to our Pump Flowrate Calculator page