Dealing With Dissolved Organic Solids (DACs) in a Pond Environment
By Ron Boedeker
Our main goal is to provide a constant and stable environment for the fish.
We divide pond water management into two main categories:
Realize that most ponds are effectively a closed system. Everything that goes in stays in, as the saying goes, “The fish live in their own toilet”. We call this build up of organic material “Dissolved Organic Solids” or DACs and our goal in achieving good water quality is to reduce these dissolved organic solids to their lowest practical level.
All living things need to have an adequate steady supply of Calcium and other minerals to meet their needs.
This is best done with frequent water changes.
Remove 15% of the water as often as possible, replace with dechlorinated water. Use a chlorine removing product or run new water thru a carbon filter to remove the chlorine.
24/7 trickle system is adding new water to the pond thru a hose or small tubing on a constant year around basis set at 5 to 10% per day. This will require an exit point for the extra water to leave the pond. It can be a simple over flow or more commonly, a sump for the exiting water to flow into and a sump pump to pump the waste water away.
We recommend not more than 12 inches of fish for each 250 gallons of pond water or better yet, 12” per 500 gallons for larger koi.
The idea is to give the fish enough food for their needs, but not more than that. Fish will eat way more pellet food than they need and the extra just passes thru their system and pollutes the pond water. Also, most ponds have plenty of algae to nibble on.
Feeding what the fish will eat in 5 minutes and remove any uneaten food.
Empty the skimmer each day to remove uneaten food.
We do not want to leave any uneaten food anywhere in the system. If left there, it will break down and contribute to the unwanted organic load of the pond.
Maintaining High levels of dissolve oxygen will break the organics down faster and can be achieved with a well-designed waterfall, large air stones or other methods.
Good circulation means that all areas of the pond have good water movement. This will prevent a build up dead or dying material from accumulating in the pond.
Effective surface skimming will catch the excess fish food, falling and windblown debris from settling in the pond. It will break up the surface proteins and oils allowing for a better Oxygen exchange at the air/water interface while recirculating the water back to the pond. The skimmer basket should be dumped out daily. An overflow system will remove the surface oils and organic permanently from the system lessening the bio load on the filters and the water column.
Plants can be both a positive and a negative on the water quality. On the positive side, they provide shade and shelter to the fish. They absorb pond pollutants and help cleanse the water. On the negative side, they absorb minerals the fish need and as the plants die off, they contribute to the organic loading of the pond. As the fish get larger, they can damage themselves on the plant pots and stands.
Plants aerate the water during the day, but remove oxygen during the night. So in a heavily loaded pond in hot weather without effective mechanical aeration, the oxygen can be depleted enough to kill fish in the early morning hours when the dissolved oxygen reaches its lowest point.
There are several things we want to keep track of in the pond water.
On the chemistry side, we need to be sure that the buffering (KH or Alkalinity) capacity of the water is adequate. If the buffering capacity is exceeded, the PH will fall, potentially causing a PH crash killing all the fish. We also need to be sure the pond system has enough calcium and minerals to sustain the plant and fish growth, so we test for GH (general Hardness) and calcium.
On the biological side, we need to watch the Ammonia and Nitrite. We should never be able to read any ammonia on a pond test kit.
Dissolved organic solids are the combination of all the organic waste in the water column. The simplest way to see them is to fill a pint jar 1/2 full, put a cap on it and then shake it. In water with very little organic content, the water in the jar will form very few bubbles and they will collapse very quickly. In heavily laden organic rich water, the water will foam up and the foam will not break down easily. Another test is to just compare the color of the pond water to a jar of city water over a white back ground.