Ponds in Spring

 Spring is an unusual time in the pond calendar. The warming temperatures provide us with an opportunity to start some much-needed pond maintenance, but can also reveal potential issues which we will discuss in the body of text below:

Water Clarity

The first and most obvious issue for many pond owners in spring will be green soup like water in our previously pristine ponds. This is caused by single cell free floating Algae and is without doubt the most common problem people have with their ponds. Algae is a plant and when the sun makes an appearance and the temperatures warm, it begins to bloom. It is worth noting at this point that the fish actually don’t mind the green water, but I think most pond owners will – As we like to say at Complete Koi & Aquatics, water quality is for the fish, water clarity is for you! 

The most effective treatment for green pond water is without doubt a UV (ultraviolet unit) clarifier. This will give you guaranteed results and is safe for ALL wildlife. The UV clarifier works by killing microscopic algae cells in the water as it passes along the high intensity light. For ponds which already have these installed and are experiencing green water, we would expect the UV lamps to have failed over winter which will ultimately need replacing. In extreme circumstances the whole UV unit may have several issues and require fully replacing.

Improved water clarity is normally visible within 2 weeks. Once you are on top of the problem and have added/changed the UV lamp, the pond should continue to run clear until the UV lamps fail again. We would always recommend getting the largest UV you can fit, as this will continually provide you with the best water clarity results. 

Another effective way of treating green water is to use a chemical algaecide treatment such as Cloverleaf – Green Water Answer, however this does come with associated risks. The Green Water Answer treatment is effective and while it is safe for general wildlife, it has adverse side effects on available dissolved oxygen within the water. This is a requirement of your fish so if you do choose to go down this route, it is imperative that you use an air pump and air stone during the treatment. It is always best to avoid using chemicals where possible so use this as a last resort. Ensure you measure your pond volume accurately which dose correctly. This will not cure the problem in the long term and instead will simply postpone the next bloom. 

Blanket Weed 

As if pea green water wasn’t bad enough, in Spring you may also begin to see a green hair like structure zealously growing from the depths. This phenomenon is caused by blanket weed (also known as thread algae) which can cling to both our ponds and fountains, bellowing up into the water as a green scum. Spores of blanket weed can blow in on the wind or may indeed arrive on the feet of birds, but it is the increased levels of both sunlight and temperature which cause this plant to bloom.

A little blanket weed is to be expected from time to time, and this can normally be taken out with a plastic rake. For persistent amounts of blanket weed we would always recommend an enzyme-based treatment such as Cloverleaf – Blanket Answer. This particular treatment is safe to use with all aquatic life including pond fish such as goldfish and Koi carp. The treatment is combined with existing pond water and added back into the pond or koi pool in specific quantities. This activates minerals and enzymes which will immediately get to work in destroying blanketweed blooms. Initially the water will turn cloudy white, however this will generally persist for less than a week. It does not require protein skimmers or UV units to be turned off during this time, and within a month of treating using Cloverleaf ALL blanketweed should be resolved.  In instances where you are plagued with blanketweed and such treatments are used, it is worth noting that this is not a permanent solution and may need several treatments a year to remain effective.


Another issue which is often prevalent in spring, is cracked, damaged and worn pipework. The cold weather of winter naturally takes its toll on many building materials and pipe work is no exception. In cold weather pipe work can become brittle. Water which naturally freezes, expands and thaws in these conditions can often result in cracks which are often seen as minor leaks, but can also be more severe. In these circumstances patch work is not recommended, and instead we often suggest careful removal of faulty pipework. These can then be replaced with like-for-like pipe work, connectors and bonded in place with jubilee clips/solvent pipe adhesive. In these circumstances it is worth taking your time in ensuring the issue is dealt with effectively and for any uncertainties seek advice from a professional.

Water Quality & Fish Health

Now on to the most important part, fish health. The FIRST thing we ALWAYS recommend in Spring is a water test to check the quality. We recommend doing these on a monthly basis anyway but conducting a water test in Spring is particularly important. Check your parameters and make adjustments accordingly. If you do not know how to do this, Complete Koi & Aquatics can carry this out on your behalf, free of charge.

Why do we do this? Fish can be particularly sensitive to poor water quality at the best of times, however in spring the fish is just coming out of its winter hibernation. The immune system isn’t fully functioning yet, and the stress of poor water quality can further weaken the fish making it vulnerable to both parasites and bacteria.

Most ponds contain low levels of parasites and bacteria at all times. The fish naturally fends these off much like our immune systems routinely defends us against common colds. When the fish is stressed, parasites and bad bacteria will naturally take advantage of the fishes weakened state allowing them to multiply rapidly which can result in issues for other fish in the pond.

Changes in your fish behaviour can include the following:

  • Clamped fins
  • Repeated flashing (itching, normally on the bottom of the pond)
  • Jumping
  • Gasping for air
  • Lying dormant alone on the bottom of the pond

Behavioural changes due to stress and thus parasite/bacterial issues are common in ALL pond fish such as Koi Carp, Sturgeon, Goldfish and Orfe. In instances where you suspect something is wrong, we recommend bagging up a live fish and bringing it in to Complete Koi & Aquatics for a microscopic scrape. This does not hurt the fish and allows us to establish what is causing the issue so we can treat accordingly.

 There are several common parasites we routinely treat for. The first and most common of these is Costia – a single cell parasite which attaches itself to the skin/gill membrane and thrives in cold water. In instances where we find Costia, we treat with F-M-G (Formalin & Malachite Green mixture). The second most common parasite are skin/gill Flukes – a worm like parasite which latches on to the fish’s skin or gills, feeding on its blood. It is often said that flukes are to fish, what fleas are to dogs. We recommend treating fish infected with flukes, with Flukasol. The other parasite we generally come across in Spring, albeit rarer is Trichodynia - a single-celled flagellate parasite which exists on the fish skin. For the treatment of this parasite we generally recommend using Potassium Permanganate. In instances where parasites become a problem, bad bacterial blooms often become a secondary issue as they colonise on open lesions of the fish. In these instances, we recommend treating the entire pond with Acriflavine, once the parasite treatments have been completed.

So, what water quality issues should we be looking out for? Well, all of them… It is vital that all water parameters are in check to improve fish health:

  • The pH should be at a neutral 7.0
  • Ammonia levels should be at 0 mg/L
  • Nitrite levels should be at 0 – 0.5mg/L
  • KH (Carbonate Hardness) and GH (General Hardness) should both be at 120 mg/L

KH (carbonate hardness) is the ponds buffering capacity for pH. Having a KH at 120mg/L will ensure that the pond remains at a suitable pH (7). GH (general hardness) is the levels of Calcium and Magnesium in the pond. Having these at 120 mg/L allows the fish to efficiently perform standard bodily functions such as osmoregulation. Having both GH and KH in check, is also incredibly important for the good bacteria in the filter, which will then better handle the ammonia and nitrite. Please note, that organisms in the pond will use these up over the course of the year and these may need topping up subject to additional water tests.

To conclude, spring can be a difficult for ponds, however with careful monitoring and proactive management you can prevent unnecessary losses. It is always great practice at this time of year to introduce a combination of good bacteria and enzymes to your pond to help kick start the water eco-system. We highly recommend using the likes of Evolution Aqua Pure Pond / Pond Bombs. These get to work immediately and promote both water clarity and pond health. A single Pure Pond bomb can treat up to 20,000L, there is no risk of over treatment and they are safe for all pond fish such as including Koi Carp and Sturgeon.

If you are experiencing issues with your pond and are unsure on the solution, do not hesitate to speak with the team of professionals at Complete Koi & Aquatics. We are always more than happy to help.

Tel: 01204 582105
Email: info@completekoi.com
Address: Complete Koi & Aquatics, Unit 4, Tonge Bridge Way, Bolton, BL2 6BD 

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