Category Archives: Pond Disease


Koi Pox; herpes virus.


Koi herpes virus (KHV), a viral disease highly contagious to fish, may cause significant morbidity (sickness or disease) and mortality in common carp (Cyprinus carpio) (Hedrick et al., 2000; OATA, 2001). This species is raised as a food fish in many countries and has been selectively bred for the ornamental fish industry, where it is known as koi. Historically, the first outbreak of KHV was reported in 1998 and confirmed in 1999 in Israel.
Since then, other cases have been confirmed in the United States, Europe and Asia (Hedrick et al., 2000; OATA, 2001; Anonymous, 2003). This information sheet is intended to inform veterinarians, biologists, culturists, and hobbyists about KHV.

What Is KHV?
KHV is currently classified as a DNA-virus belonging to the virus family Herpesviridae (i.e., a herpes virus). Although there has been some scientific discussion regarding the accuracy of this classification (Ronen et al., 2003), more recent work (Waltzek et al., 2004) shows strong evidence that KHV is indeed a herpesvirus, based on morphology and genetics. KHV disease has been diagnosed in koi and food fish carp (Hedrick et al., 2000; OATA, 2001). Other related cyprinid species such as the common goldfish (Carassius auratus) and grass carp (Ctenopharyngodon idella) seem to be unaffected by KHV. As with other herpes viral infections, KHV is believed to remain in the infected fish for life, thus exposed or recovered fish should be considered as potential carriers of the virus (OATA, 2001).
KHV disease may cause 80-100% mortality in affected populations, and fish seem most susceptible at water temperatures of 72-81°F (22-27°C) (OATA, 2001). This viral disease affects fish of various ages, but cohabitation studies show that fry have a greater susceptibility than mature fish (Perelberg et al., 2003).

What Are the Signs of KHV?
Clinical signs of KHV are often non-specific. Onset of mortality may occur very rapidly in affected populations, with deaths starting within 24-48 hours after the onset of clinical signs. In experimental studies, 82% of fish exposed to the virus at a water temperature of 22°C died within 15 days (Ronen et al., 2003). KHV infection may produce severe gill lesions and high mortality rates. In some cases, secondary bacterial and parasitic infections may be the most obvious problem, masking the damage caused by the primary viral infection. Behaviorally, affected fish often remain near the surface, swim lethargically, and may exhibit respiratory distress and uncoordinated swimming.

Koi Pox External signs of KHV may include gill mottling with red and white patches (see picture) (similar to Columnaris disease), bleeding gills, sunken eyes, pale patches or blisters on the skin. Microscopic examination of gill biopsies often reveals high numbers of bacteria and various parasites (Hedrick et al., 2000; OATA, 2001; Goodwin, 2003).
Internal signs of KHV are inconsistent and non-specific, but they may include adhesions in the body cavity and a mottled appearance of internal organs (Hedrick et al., 2000; Goodwin, 2003).

How Do Fish Get Infected with KHV?
The herpes virus that is responsible for KHV seems to spread in the same ways as most herpes viruses. Methods of transmission include direct contact with infected fish, with fluids from infected fish, and/or with water or mud from infected systems. Depending upon water temperature, fish that are exposed and susceptible may become infected and either develop the disease and die or become carriers of the virus (OATA, 2001). Goldfish and other fish in the carp family are not susceptible to KHV disease, and they do not appear to act as carriers of the virus (Perelberg et al., 2003; Ronen et al., 2003).

Level One UV Sterilization is very effective against this virus and although not a treatment for infected fish, a properly installed/quality UV Sterilizer should be employed for prevention.
If your pond (or aquarium) already has a UV Sterilizer, it is also imperative to change your UV Bulbs every six months for level one UV Sterilization maximum effectiveness.


*Pond Care Information
An easy to follow article about pond care with many more in depth resources as well as product resources cited

*Aquarium Lighting Information
An in depth article that I recommend and have found to be the most up to date anywhere. It includes information about the many types of lights including LED Aquarium Lights.

*Aquarium Chemistry
Probably the best article on the subject of aquarium chemistry I have found. The author gets it right with the science behind electrolytes, GH, KH and more

Copyright 2019, By Steve Allen



Copyright 2014, By Steve A
Revised 10-18-19

I am using this article for the first “aquarium article digest” entry as this seems to be an area of aquarium/pond keeping with MUCH misunderstanding, and even as of the most recent revisions, continues to be if not more so than when I first wrote this article in 2009.

Ultra violet ‘C’ sterilization is a process that is one of the most effective means of disease prevention in aquariums and ponds and for general water quality control in aquariums and ponds.
A correctly installed, quality UV Sterilizer helps provide and improve a fish’ chances in fighting difficult diseases such as ich even though UV Sterilization is less effective directly in destroying this disease pathogen.
See this example of an online seller of good to premium quality Sterilizers: Aquarium & Pond UV Sterilizer

Aquarium UV Sterilizer Clears OxidizerPart of the reason for aid in fish immunity, is that UV Sterilization is that the UVC irradiation which is contained in the unit will break down oxidizers in the water column that would otherwise lower a fish’ immunity (Redox Balance), this aspect is often missed as many persons use only focus on the germicidal/algacidal properties of UV Sterilizers.

This not only has been proven in controlled tests by gurus in aquarium research such as Carl Strohmeyer, it is easy to demonstrate by adding an oxidizer such as Potassium Permanganate that colors the water and running a level one UV sterilizer against a control aquarium with none (all parameters, bio load, etc. otherwise equal) and noting the considerable speed the Potassium Permanganate is cleared from the aquarium utilizing the UV Sterilizer.

The photo to the above/right demonstrates this.
Credit: Aquarium & Pond UV Sterilization | How to use a UVC Sterilizer

Further Reference: Aquarium Redox Balance

Please read this article for more about this subject:
“Fish Immune System and UV Sterilization”.

Unfortunately many aquarium/pond forums also focus only on the aspect of irradiation of disease (which can be hit or miss depending upon installation and UV quality), but miss the aid UV Sterilizer provide in improving Redox balance.
Many of my friends in the professional aquarium & pond maintenance business have cited many times that a new customer would call them out for help complaining the UV Sterilizer they purchased elsewhere was useless, but after investigating these professionals would find that the UV was of poor quality and/or incorrectly installed.

This has been especially common of late with the influx of low quality UVs such as the Green Killing Machine, Submariner, Jebo, AquaTop, and many others which is what you get for under $50 on eBay or Amazon, as well as some of the many low end online retailers.

The unfortunate aspect of purchasing these low end UV Sterilizer is that these are not really sterilizers at all, rather just clarifiers.

So what often happens is a person purchases one of the cheap UV units, then sees no improvement in fish health, then goes onto some aquarium forum, Facebook, Youtube, Yahoo Answers, etc. and reports that the device was useless.
The problem is the devise they purchased was useless for true level one UV Sterilization, but the process and the concept is not.
This very common problem is analogous to purchasing a thin plastic tarp to cover ones swimming pool and then when a child still falls in, stating pool covers are junk, when in fact a pool cover designed for protecting children from the pool should have been used and would have worked!!

Excellent video on the subject:
Do I really need a uv sterilizer
Do I Really Need UVC?

What are we looking for to properly utilize UVC energy for irradiation?

  • Water flow rate through the UV Sterilizer. This is often expressed as “gallons per hour” or gph per watt of UVC energy
  • Dwell time (related to flow rate). This is the time the water stays inside the UVC irradiation chamber
  • An actual High Output (HO) low pressure UV Lamp/Bulb. The difference between the more commonly used medium pressure UV lamps is as much as FOUR TIMES the UVC output. Even in a less expensive Chinese built UV Sterilizer this can mean the difference between a TRUE UV Sterilizer and a UV Clarifier.
    Most sold via Amazon and other discounters DO NOT utilize HO UV lamps.
    Further Reading: Actual UV-C Emission from a UV Bulb; Aquarium or Pond
  • Water Turnover in pond or aquarium per hour. This is how many times per hour the water is passed through the UV Sterilizer as per a given unit of water in the aquarium or pond
  • Distance of UV Lamp from UV Sterilizer containment ‘wall’. This should be no more than 3 mm, which many “built in” canister aquarium or pressurized pond UVs are much greater than.
  • Temperature of water. UVC is effective is between 20 C (68 F) and 40 C (104 F)
  • Pre-Filtration including Turbidity of water. Particulates in the water can & do have a affect the ability of the UVC to damage or destroy pathogen, algae, or reduce oxidizers (Redox)


There is a lot of new evidence as to the benefits of UV sterilization for ALL fish, and many myths have been dispelled such as “UV Sterilizers destroying beneficial nitrifying bacteria”.
I will try and present material in as readable a format as possible, rather than get down to too much scientific jargon that is difficult for many to understand as many facts can often be presented without every technical term applied.

UV Sterilization is also effective for controlling suspended algae (green water) in ponds, along with proper filtration such as Veggie Filters/pressurize filters, please see this article:
“A Clear Pond; pond information”.

True Level One UVs are also useful in Reef aquaria, especially new ones where the chance of disease introduction is high, as well the UVs help in keeping a balanced Redox Potential which is useful for disease prevention via boosting the fish’ own immune response.
As the reef aquaria ages the sterilizer can be placed on a timer or turned on and off as needed (although I still recommend running 24/7 in many reef aquariums).

As for the Redox Balance, this is an often overlooked aspect of both freshwater and saltwater aquarists that HAS BEEN PROVEN in well funded studies to aid in immune response.
Unfortunately some aquarium forums choose to ignore this science or push low end UVs (often under $50) that cannot product level 1 UVC

The Redox Balance is basically the oxidation and reduction properties of water.
This is VERY important for proper breakdown of organic waste (the oxidation side of Redox)! Especially in aquariums where the fish/invertebrates come from waters of low turbidity (African Cichlids) or tend to produce a lot of waste (Goldfish).
“Most experts now agree that the Redox should be +300 to -100 mV for marine or +125 to -200 mV for freshwater for healthy fish immunity, which a UV Sterilizer can help maintain.”
Used with permission From: “Aquarium & Pond UV Sterilization

For more information about the Redox Potential, please reference:
Aquarium Redox Balance

Further Reference: UV Therapy

Anecdotal Arguments Against

One argument against UV Sterilizers in ponds is that they are not natural, but for the clarity most persons want out of their pond, this is not possible without either UV sterilization or a flow thru stream (although many persons with well planted, well shaded ponds do well with clarity too, but UV Sterilization further compliments these ponds too).

Many articles I have read state that a UV is not that beneficial to an established aquarium as a healthy aquarium depends on beneficial bacteria typically growing on media in your filter which neutralize ammonia.
Unfortunately the problem with this statement is beneficial bacteria belongs in the filter, not in the open water column which is all a UV Sterilizer effects.
Also this may work well for some advanced aquarists who are not adding fish and have a healthy Redox Potential/Balance, but not in the real world of average and above average aquarists that I and many of my friends have dealt with in the 100s of aquariums they have serviced.

Also it is noteworthy that an aquarium is a closed system, NOT OPEN, so inputs of added buffers, minerals, Redox reducers, etc are necessary.
The use of level 1 UVC irradiation is just one more of these inputs since Redox Balance has been scientifically proven to improve with the use of level 1 UVC.
The problem is often these persons stating they used a UV Sterilizer with no improvement in fish health, were likely not setting up the UV correctly or more likely, were using one of the many cheap UVs flooding the market such as the JBJ, AquaTop, Green Killing Machine from sellers such as Amazon.

Some Recommended Aquarium UV Sterilizers

  • AAP/TMC Vecton & Advantage Level 1 & 2 Capable UV Sterilizer
    There are simply NO BETTER UVs than these. TMC made a name for themselves with these decades ago and are still the best value (yes Aqua Ultraviolet & Emperor are also good, but these still fall short in dwell time and value
  • AAP Terminator UV Sterilizers
    While an economy UV sold under many names, these have a HO UVC Lamp that most other Economy UVs do not
  • AAP Submersible/Internal UV Pump/Filters
    While this style is not as efficient nor as long lived, it is very user friendly. Once again the AAP models is different than most in that it utilizes a HO UVC lamp along with adequate Pre-filtration that most others do not

Aqua UV versus TMC UV Sterilizer
Aqua Pond UV vs TMC AAP Pond UV Clarifier Sterilizer


UV Sterilizer maintenance is quite straight forward; make sure you keep your unit dry on the outside, if used for a pond try and protect your unit from harsh weather (most sterilizer can withstand the outdoor environment, they just last long if they can at least be partially sheltered).

Change your UV bulb every 6 months for aquariums, and also every 6 months for ponds in warm climates where there is no winter freeze.
In cool climates a pond UV bulb can be changed every season (usually late spring/ early summer).
See: High Output UVC Replacement Lamps

For a full in depth article on this subject:

How UV Sterilization Works, For True Level 1 or 2 in Aquarium/Pond

The above article should be read for much better understanding of how to correctly use your UV Sterilizer.

Unfortunately with the Google Search of late mostly becoming a Spam search for (not “the spruce”), and others; GOOD RESEARCHED articles such as the one above are more difficult to find, but I urge my readers to read this article in full, then read it again (and maybe again until you understand the concepts presented!!
Do NOT purchase a UV Sterilizer UNTIL you read the above article

If you do decide to purchase a decent UV, not just some cheap toy calling itself a UV Sterilizer, consider this website that a professional in the industry I know with 3.5 decades of experience in UV Sterilization owns:
Good to Premium UV Sterilizers for Aquarium or Pond


*Aquarium Lighting
An in depth article that I have found to be the most accurate and up to date anywhere. It includes information about the growing in popularity LED Aquarium Lights.

*A Healthy Aquarium, Disease Prevention
An excellent step by step scientifically tested/proven method to keep a more disease free aquarium

*Aquarium Ich: Ichthyophthirius Multifilis and Cryptocaryon Irritans

*FISH COLUMNARIS | Fungus & Saprolegnia | Treatment & Prevention

*Pond Algae

*Pond Care, Information

Copyright 2019, By Steve Allen