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Navigating Springtime Challenges for Fish Health in Ponds and Water Gardens

by Joe Cadieux on January 05, 2023

Spring-time Fish Health:

Spring is an arduous time for fishes everywhere.  The changing environment puts a great deal of stress on all of our aquatic creatures.  These changes include temperature, microbiome, and the concentrations of dissolved solids that will rapidly fluctuate changing the basic water chemistry during this season of change.

As the snow melts (or the spring rains come) many a soluble minerals and compound flows into our ponds.  Be it 10,000 acres or 2500 gallons, these inputs change the environment drastically in the spring of the year.  Small systems (private ponds and water gardens) get the hardest hit because they do not have the environmental inertia that large waterbodies have.  That is: a lake of many millions of gallons of water can absorb the dissolved solids more readily without effecting a massive change in water chemistry due to its buffering capacity.  Said another way, due to its massive volume it takes a much greater volume of solutes to change any of the chemical attributes of that waterbody even a fraction of a point.  Small ponds and water gardens aren’t so lucky.  Every rain shower, snowmelt, and wind-blown event can introduce a difficult situation for the fish attempting to shed their lethargy after a long winter.

As the water warms, the macrobiotic (and macrobiotic) community awakens and effective changes the pond environment.  As different organisms (bacteria, insects, protozoa) become more prominent their biological functions change the environment as they grow and reproduce. This is a fancy way of saying, these critters grow up, mate and die…… all effecting the water quality in different ways.

The biggest issue in spring is the rapid fluctuations of water temperature.  Large waterbodies like lakes have a thermal inertia that allows for a slow rise in temperature allowing an easier transition into spring.  Smaller ponds and water gardens heat and cool rapidly.  Every day this spring a water garden of 5,000 gallons a can heat and cool 10-20 degrees every day until the weather stabilizes in summer.  A good example is this past week here in the mid-west.  We had a beautiful 70degree day which heated up water temperatures into the low 60’s.  This gorgeous chamber of commerce day was followed by a typical Midwestern spring day of 35 degrees and raining.  This quickly dropped the water temperature back down into the high 40’s.  As warm blooded humans, we just grumble about these rapid changes, curse our rotten luck and desire to live in such a climate and move on (mostly with help of adult beverages).  Any-hoo….. As exotherms, fish and amphibians take these changes very hard.  Many rapid temperature swings put major stress on the swimming creatures and can leave them vulnerable to infection and reproductive distress.

So those are the hurdles, here are some ways to help our wee swimming companions usher in a bountiful spring of joy and frolic-ish-ness.

Always do your spring clean-out either well before, or a good deal after the rapid spring temperature fluctuations.  Around here in the northern Midwest its early April or wait until June.  My preference is early spring as cold water is the best environment for healthy fish.

Be sure to use a cold-water bacteria product like (Crystal Clear Spring Prep) from the time the ice goes out (water temps of about 40deg) until you can start with your summer blend at around 55deg.

Be aware of the behaviors of your fish.  If all of the koi and gold fish are active and one is not, it may not be doing so well.  Maladies usually manifest as bacterial infections and present as lesions on the bottom of the fish or near the gills.  If you can isolate the infected fish, and inoculate with appropriate medications (like this CrystalClear KnockOut Plus CC136-16 to CC136G) it is very likely that your precious finned friend can pull through with flying colors.

Make sure to add (or maintain) your pond salt (salinity) levels at near 1ppt.  (Pond Salt) This will fortify your fish with a healthy slime coat to ward off infections and insulate them from parasitic invasion. Your fish can tolerate a much higher level (>1ppt) of salinity, alas your plants will not, and you need those plants later on to help out the pond during the summer, so keep the levels at about 1ppt, and all will be well.

Every pond has a carrying capacity for fish, if you are carrying too many fish, the biota gets all gummed up and you end up with fish health issues among a host of other management problems. So as a rule of thumb: 1” of fish for every 10 gallons of water in your water garden. It is important to note that there is a finite amount of resources available in a small pond environment, and the more fish-mass you pack in there, the more health issues you will encounter.

Alas, there is only so much one can do to sooth the passage into spring. Many a memorial service will be performed for our fallen Osteichthyes brethren as sometimes the world is not enough and they must swim through the cosmos back from whence they came. To join the circle of life, or fertilize a tree…. Whichever.

Thanks for reading


Senior Biologist