Aqua Production Systems
Keeping it Clean
Whether it is at home or an industrial sized tank, cleaning is a critical component of fish health. We clean the water, we clean the tanks, and we clean the building. Here are some tips for effective cleaning....
It is much easier to detect and solve issues in a clean environment rather than one camouflaged with clutter, dirt, or standing water. Indeed, cleaning is an area where prevention pays big dividends.
Three fundamental guidelines for cleaning a tank are the following:
In a marine operation, fresh water is a very effective cleaning agent.
In freshwater aquaculture, a saturated brine solution can serve as an effective cleaning agent.
For thorough disinfection clean with an acidic cleaning agent, followed by a base.
Here is a collection of suggestions for cleaning specific items of a holding tank.
Tanks & Troughs
Tanks are often designed for self-cleaning. Those that aren't may need regular cleaning- a process that requires many man-hours.
Larval tanks, for example, often have flow patterns that are not self-cleaning. In these cases, daily removal of solids may be required. Scotian Halibut has developed a larval tank automatic cleaning system that collects solids from the bottom of the tank and directs them to the center drain.
But even self-cleaning action in the tanks doesn't always translate to self-cleaning action in the drains. A common drain cleaning method is to flush the drains by pulling a standpipe or opening a drain valve momentarily. This can be done daily or 4-6 hours after every feeding.
After a tank is emptied, a thorough clean to remove bio-film from all surfaces is necessary. Scrubbing with freshwater or a pressure washer is often adequate in a marine facility. In larval tanks or fresh water tanks, a disinfectant agent should be used as a secondary cleaning step.
Solids that gather in recirc systems and are not routinely cleaned allow bacterial counts to increase. Sludge in RAS has been linked to off-flavors in fish cultured in these systems. My first day on the job, I was in a marine recirc reservoir scrubbing biofilm and sludge off the walls and floor.
Enclosed tanks, or tanks with high sides, should not be cleaned by lowering people inside without first taking precautions to remove any hydrogen sulfides in the tank. Hydrogen sulfide is heavier than air and will replace oxygen at the bottom of the tank.
Equipment & Filters
Equipment and filters often require cleaning as part of a regular maintenance regimen. Back-washing sand filters or heat exchangers for example. Even with regular back-washing, sand filters on effluent streams can become channeled with biofilm and require more than a typical backwash. Scotian Halibut has developed a method of injecting compressed air through the sand bed as a way to remove biofilm from the sand particles.
Pipes & Fittings
Biofilm or biofouling in a pipe may need to be cleaned periodically. There are a few effective methods for this.
Where possible a pipe can be allowed top lay fallow long enough for any growth to die from lack of oxygen. Flushing the pipe will then remove the majority of organisms.
A pipe can also be cleaned with a high-pressure hose. Nozzles that rotate and pull themselves though the pipe are effective at this. But the pipe has to be designed and built or modified to allow such access. PVC 'cleanout' fittings are a cost-effective and simple way to add this feature to a piping system. Be sure to check the pressure rating on the cleanout before buying to make sure it is suitable for operation in your system. Many cleanouts are built for drain applications only, not pressure applications.
Pipe cleaning can be done using a slow flush of various solutions. In a fresh water operation a saturated brine solution is often effective. In a seawater facility, fresh water may be sufficient. Sodium hydroxide, bleach, hydrogen peroxide, citric acid, or high ORP water have all been options used successfully at various times.
Pipe carrying air may collect condensate in low spots and provide an opportunity for non-desirable organisms to grow. The ideal solution is to provide a vertical condensate trap where low spots exist. This could be as simple as a valve at the bottom of the low spot for periodic purging. Alternatively, disinfection can be achieved by injecting ozone through the line during a shut down period if the risks of exposure to staff can be mitigated.
Floors & Walls
Keeping floors clean is both a bio-security and worker health and safety concern. Holding facilities may often have indoor environments conductive to growth of biofilm, meld and fungus.
Frequent wash-down of walls and floors with a pressurized hose is a good preventative measure and should be done after any splashing of culture system water occurs or is thought to have occurred.
A thorough scrubbing of floors with a mild cleaning agent such as dish soap should be done monthly, being careful to keep any such substance below top of the tank walls.