UV Sterilisers, Sizing and application rates

There is plenty of information out there on dose for various organisms for effective sizing and treatment of pathogen. I have a list of over 100 myself.

Note, before we begin, I will use both uws/cm2 and mJ/cm2 to reference dose rate, to give you a guide, 50,000uws/cm2 is the same as 50mJ/cm2.

Of these pathogens that there are known dose rates for, 76% percent of them can be treated with a dose rate of 30mj/cm2 or less.

The majority of these organisms are bacteria and fungi with some viral and simpler parasites thrown in, but the point here is, even a UV applied at 30mj/cm2 has a significant effect on the reduction of the pathogens and potential disease causing organisms due to bacteria being most prevalent in the aquatic environment.

In a nutshell, if you knock out 76% of the organisms that could potentially cause issues in your system, you are well on the way to creating an environment that the culture species can thrive in without a lot of stress.

Of course this is just the number of organisms we have dose rates for that fall under 30mJ/cm2, not an representation of the actual prevalence of these organisms in any given body of water, but as we know bacteria are by far the most dominant organisms, and that removing these can reduce stress significantly, its worth noting this and also how easy they are to treat.

First before I get into the real quagmire of UV application I want to address something very important.

THERE IS NO CONFIRMED DOSE RATE FOR SALTWATER WHITESPOT! - Stop using 280mJ/cm2, just stop.

This is a subject I come across almost daily, and that is the dose rate of 280,000uws/cm2 (280mj/cm2) to treat saltwater whitespot (Cryptocaryon Irritans).

And here is the number 1 reason.

That dose rate of 280,000uws/cm2 comes from a Tropical Fish Hobbyist column in the 1990's (or maybe even earlier), and some other publications that have extrapolated dose rates from freshwater whitespot.

The authors in question extrapolated the size and dose rate of freshwater whitespot to Marine whitespot (marine whitespot is a physcially larger organism)

The KNOWN dose rate for freshwater whitepost, Ichthyophthirius, is 100,000uws/cm2) this has been verified by independant studies.

Firstly, extrapolating size and the dose rate is not how UV dosage works, it completely depends on the organism, the cell structure, the point of the lifecycle, etc.

Secondly, there has not been to my knowledge, any actual study done on eradication of the saltwater whitespot organism with UV in a peer reviewed study to determine an exact dose rate.

So what am I saying here...

Well let me start by saying, could this dose rate work? Well at this dose rate, being inside that reactor tube wouldn't be unlike standing a mile from the surface of the sun, so yeah, it probably would work.

But does it need to be this high?

The question of the size of the UV verses space, flow rate, and price is a common one.

And whilst you might draw a very logical conclusion that buying a car to simply do driving around town might be similar weather you buy a hatchback or a ute, buying a Combine harvester to go and get the groceries on a weekly basis or pick up the kids from school, is not only unnecessarily costly, its a bit OTT.

A UV delivering this dose rate is ludicrously large compared to the amount of water it is treating, and in most cases is simply not economical.

So now that Ive picked that apart you might be asking, how does this help me Gareth?

Well firstly, my opinion is that this dose rate of 280mJ/cm2 shouldn't even be published, I don't use it, and I wont until I at least see a study confirming its accuracy.

I can say that I have applied a dose of 100-110mJ/cm2 to prevent the spread and to treat saltwater whitespot (Cryptocaryon Irritans) on countless occasions with great success.

In most cases, application of this dose rate occurred in multiple tank systems, where 1 tank experienced an outbreak of saltwater whitespot and it did not spread to the other tanks.

The water was treated through the UV on the return to the tanks after mechanical and biological filtration. The pathogen was also treated completely within 10 days give or take, again without spread and without the application of chemotherapeutic treatments.

I have experienced this many many times, and is generally the dose rate I default to for marine systems requiring a higher level of biosecurity control. It also doesn't result in a diabolically massive UV, so that is a plus.

There is another similar dose rate getting around, especially in the Aquarium and Aquaculture sectors, of 180mj/cm2 for aquarium application or for "parasites".

If this dose rate is determined from the same list I work from (and often the list others work from is smaller), then between 100mj/cm2 and 180mj/cm2 there are the following organisms:

Brooklynella - 126mj/cm2 (log 3 reduction 99.9%)

Flavobacterium psychrophilum (Salmonid Bacterial Coldwater Disease) - 126mJ/cm2 (log reduction unknown)

Vibrio sp. (oyster) - 155mJ/cm2 (log reduction unknown)

Trichodina Nigra - 159mJ/cm2 (log reduction unknown)

Saprolegnia diclina (zoospores) - 170mj/cm2 (log reduction unknown)

Rhisopus nigricans - 111mJ/cm2 - 200mJ/cm2 (log 1 reduction 90% to log 2 99% reduction)

The prevalence of these diseases in normal culture is very low, and some are even species specific, or occur on some species more often than others. This makes me question if this is a good reason to straight out apply a UV at this dose rate, based on numbers of organisms treated, the prevalence of those parasites, and the size of UV required to do it, my opinion is a dose of 100-110mJ/cm2 is much more suitable for a "parasitic" treatment.

In this case if I was to encounter any of the above organisms, I would simply reduce the flow rate by way of the bypass in order to increase the dose rate for the time it takes to remedy the issue. Or, if i was treating specifically these organisms as they were known to high a high prevalence in that particular culture system, size the UV specifically to that.

Application specific turnover and treatment rates

A common theme you will see in the below is the application of a turnover rate verses the speed at which an organism reproduces.

Interrupting that will produce a net positive gain by eradicating the organism by beating it at its growth rate, to put it simply.

The other, is that the application rates have caveats, such as water cleanliness (level of TSS in the water), water clarity and organic carbon levels, amoung other things.

Ponds and general clarification (side loop) - 1 total system volume (tank, sump and filtration volume) every 3-4 hours @ 30mJ/cm2.

This is due to algae generally reproducing every 5 hours approximately, and so by interupting the life cycle by treating the whole system volume at rates faster than this you can kill the algae faster than it can reproduce.

In clean systems with low organic carbon and waste levels, this is also generally effective to treat bacteria, and can be used in ponds and aquariums as a base application rate, NO LESS THOUGH!!

Aquariums and Aquaculture systems (side loop) - 1 turnover per hour of the entire system volume (tank, sump, filtration, total) through the UV at the appropriate dose rate for your application

Minimum dose rate - 30mJ/cm2 for bacteria and algae

Good middle of the road dose rate - 60mJ/cm2 (will kill everything 30mJ/cm2 dose plus, from observations, effective against a good range of viral and fungal infections)

Parasite treatment - BTA's benchmark, 110mJ/cm2 (126mj/cm2 if clownfish suffering from brooklynella is a concern, highly recommended for retail aquarium store systems carrying clownfish)

If you have a specific organism you want to treat, you should speak to a UV professional to size a UV appropriate to treat that organism.

A very good friend of mine and aquarium business owner in Australia, on my recommendations applied UV sterilisation at 110mJ/cm2 on a side loop processing 1 turnover of the system volume per hour for 2 reasons:

- we determined we simply didn't have room for anything else

- budget was a concern as there were 4 being put in

Mortality rates reduced dramatically and the application rate proved effective for control of bacterial and parasite infections long term.

There are 3 very important things to remember for applying UV on a side loop in aquarium and aquaculture systems

Solids filtration is important because of particles shading organisms for treatment.

Organic carbon at elevated levels will help bacteria to proliferate and decrease effectiveness, the less bacteria to treat, the less disease will present, and the better a UV can target potential pathogens at lower treatment rates.

Tannin's in the water and low clarity effects how well UV transmits into the water. the cleaner the water, the better a side loop UV application will work.

You could reduce this to 1 turnover every 2 hours of the entire system volume if you have low organic levels, low tannin's, high clarity and sufficient mechanical filtration.

This is mostly in relation to bacterial proliferation and the treatment of bacteria, heterotrophic bacteria as a generalisation will reproduce every 30 minutes, and the more organic carbon in the water, the more they can reproduce.

In aquariums this is mostly easy to achieve, in Aquaculture systems I would recommend the application of ozone to maximise effectiveness of a side loop UV.

This application rate is best applied with other biosecurity measures in place such as dipping, pre treatment with chemotherapeutic's and above all, quarantining of your fish before transfer to your main system.

If you don't quarantine your fish, know this, I will find you.

Aquariums and Aquaculture systems (total return treatment) - this is treating all of the water being returned to the system through the UV at the determined dose rate

This of course is the most effective treatment, as you can assume with a fair margin of safety, that all water returning to the tanks is treated with UV and therefore there is no short circuiting of the water and no water goes untreated and potentially gets circulated back to the system untreated and laden with pathogens.

It does however mean that the size of the UV is exponentially larger than on a side loop treating on 1 volume turnover per hour, assuming of course that the turnover rate is multiples of the system volume rather than a percentage.

If its less than 1 turnover per hour, then you are in a good spot to apply a very effectively sized UV, and a flow rate that isnt going to break the bank and treat all the water on the return, fist bump!

Minimum dose rate - 30mJ/cm2 for bacteria and algae

Good middle of the road dose rate - 60mJ/cm2 (will kill everything 30mJ/cm2 dose plus, from observations it is effective against a good range of viral and fungal infections)

Parasite treatment - BTA's benchmark, 110mJ/cm2 (126mj/cm2 if clownfish suffering from brooklynella is a concern)

This also means you can reduce the flow to increase the dose and still maintain an effective application rate, mostly.

For instance, if your turnover rate is 3x per hour, and your application rate is 110mj/cm2, you could cut the flow by 2/3rds using the UV by-pass, still maintain a 1x per hour treatment rate equal to a side loop application, and achieve a 330mJ/cm2 treatment rate.

Not that a treatment rate that high would likely ever be needed, but for demonstration you can see the flexibility of this application.

So, the Nutshell

Can you economically apply a UV steriliser to your aquarium or aquaculture system for biosecurity control, at specific dose rates, on a budget or where room is concerned.....? YES, yes you can.

Should you.... yes

How you do you determine which route to take, well that's what we are here for, to help you work that out.

BTA Partners with Advance UV, an Australian manufacturer of UV steriliser's that has been designing and manufacturing UV's for nearly 30 years.

We have you covered for UV's in freshwater and Saltwater, for all flow rates and system types.