As you're all aware, there are severe water restrictions in the PE metro and surrounding areas.

The past week we had a spell of bad heatwaves to top it all off with. On Tuesday the temp in PE was 36C. The morning before work I fed my koi and the water was as clear as swimming pool water (literally). When I got home around 15:30, the water was so green that I couldn't even see any of the koi. Never in my life had I experienced this.

I don't use UV lights on my ponds but this time I quickly made a plan to include one on the return to the pond. I split the original 1 return into 2 returns with a T-connection and put a ball valve on the pipe leading to the UV in order to regulate the amount of water that flows through the UV and to enable me to bypass it completely if needed. The other return was kept as it was with no ball valve to regulate the flow.

My question here is:
With the ball valve being open halfway, will the water still be clarified in a few days or should the complete waterflow from the filter systems flow throught the UV?

I was told that the slower the water the runs through the UV, the better it clarifies. It's for this reason that I split the return and am regulating the amount of water running through the UV.

Sourced from the Ultra Zap website:

To maximise germicidal action it is important to consider the contact time and the contact distance between the U.V.c source and micro-organisms to be treated. The contact distance is set by the design of the U.V. steriliser. You should bear in mind that the larger the diameter of the steriliser, the greater the dwell time of the water resulting in an increase in the dosage. However, as the radius of the steriliser increases, so does the distance the radiation must travel. This causes a decrease in the generated dosage.
The actual time it takes for the water to pass through the chamber –‘the contact time' – is a function of the recommended flow rate per tube. The overall volume of water in the livestock tank or system, and the frequency that the total volume comes into contact with the U.V. source, is also significant and must be taken into account for the correct operation of the filter on a given system

Flow rates given by Ultra Zap

SIZE POND CAPACITY MAX FLOW PER MINUTE
8 Watt 6 000 Litre 40 LT/M
15 Watt 15 000 Litre 60 LT/M
30 Watt 30 000 Litre 140 LT/M
55 Watt 55 000 Litre 300 LT/M

My pond (30000L) is in full sun with only the wooden bridge providing some shade. I use 3 x 55W UV’s and it took about 6-7days for the water to become crystal clear.

I use the UV’s in parallel to obtain a longer contact time with the water. The main thing is not to exceed to maximum flow rate that the manufactures specify. I use a 75mm pipe coming from the pump and it splits up via a 50mm T-piece. The one side goes to the 3 x UV’s and the other end goes to my filter system. This is also the point where I fitted a ball valve to control the flow via the UV’s. The only reason I did that was to get more water to my filters since you get a lot of restrictions via the UV setup.

In your case you must just be careful to turn UV’s off when you close the valve since you might damage the UV when it runs dry.

Since my pond is in full sun, I prefer to use a larger than normal UV setup to keep water clean. On my previous visit to SA I installed a 20W UV on my small QT pond but the water is not clear, so I will replace it with a 55W Ultra zap. If your pond gets some shade I am sure the smaller UV will work, but in my case it is a waste of time.

I had my UV switched off for a few months but started getting algae problems in the heat and the funny rain pattern, so had to switch it on again. In fact, I have ordered 3 new tubes this morning – an expensive little purple light but hopefully it will do the job again.

I have 2 options to cover my pond. Aluminum roof where you can open or close the panels (R900 a square meter), or a canvas structure (same as the carports at some shopping centers ) Far cheaper at R5200 for a 6.5 x 3.5m structure

A day or 2 after UV installation


Week or so later

I installed a 15W unit on the 14000L pond. I'm sure this will work but might just take about 2 weeks.

I used this 15W unit since it was given to me and I don't see the point in purchasing another one if I have one that indicates that it handles 15000L ponds.

I know that it's advised by some keepers to use one that can handle double your pond capacity but I'm sure that's just if you want it to be even more effective and work faster..... ie. for the more impatient people.

I'm assuming that the setup I've got will clear the water in due time??

This is my 5 cents worth.Boys ,Boys I might be still a beginner with the Koi's [/b]BUT there are basics that each and every koi keeper must follow. There is no short cuts. It is black or white no grey. It starts with the love of the hobby, the correctly builded pond,the correct filter system,the correct flow of the water, the right equipment like the UV lights AND LASTLY the effort that goes with the live long journey. If you not 100% commited to this then rather pack up and leave.

We all know this!! People are here to help and not critisize. I never needed UV lights and wanted feedback. Trust me when I say that I'm 100% committed, even my wife complains about all the attention the fish are getting. There's no need to insinuate that I wasn't committed because I don't see the point in buying a bigger UV...

Chris on a 40000l pond I am using 2x 55W UV lights feed by one .75kw pump, water is clean......well now it is needed to add the second light (this was a previous discussion thread). The flow rate is the all important key here, you can get some flow rate calculators.......don't trust what it says on your pump.....

Chris, your setup sounds fine - nothing wrong with it.

Regarding the sudden green water. That means that there is a source of food for the algea somewhere. The sudden heat was just the last part of the formula to bring it on - I would investigate that if i where you.

Just something to take into considuration: If you are having to cut back on water changes due to water restrictions then also do that accordingly with the amount food you feed.

Try and keep the oxygen levels higher than normal if your pond is going to more dirty than usual.

The UV will work, it will just take a bit of time. There is an optimum amount of flow. You want to destory the algea slightly quicker than what it is being created. So dont use a to slow turn over through the UV.

Im sure you can work it all out.

How about some pics?

Hi Chris.

I am very sorry if you think I critisize you. I want only to make my point by saying there is no short cuts when it came to Koi.

Again I am sorry.

I've managed to get hold of another 15w UV light. I now have x2 15w UV's on a 14000l pond. Water flows through 1 into the next and then returns to the pond.

Quote :

The actual time it takes for the water to pass through the chamber –‘the contact time' – is a function of the recommended flow rate per tube. The overall volume of water in the livestock tank or system, and the frequency that the total volume comes into contact with the U.V. source, is also significant and must be taken into account for the correct operation of the filter on a given system

Keeping this quote in mind... is it correct in saying that 60l/m (on 15w) is suggested to get the ideal "contact time" for the water flowing over the UV?
If so, can I now increase the flow rate throught these two UV's as the "contact time" is now also increased?

That is right, if the UVs are connected in serial then the contact time is longer and you can speed the flow up.

But im now sure if 2 x 15w uvs = 30w UV in length. So im not sure what the flow can be increased to.

W