I have a small 18 gal. unfiltered tub pond and It was in the full sun in my backyard in the summer last year. I also had a algae problem. It is on rollers so I moved it to the front yard where is did not get lots of sun maybe 3-4 hrs at most.
The algae is controled by a product I bought made by Kordon AlgaeQuel.
direction are as follows:
10 gal- 6 drops
30 gal- 18 drops
60 gal. 1tsp.
dose every 3 days til algae in controled
I use 10 drops every 3 days til contoled,This however will kill any snails you may have. The plants are fine and so are the endler hybrids I have in my pond.This product works well but follow the directions carfully on the back of bottle.
Algae bloom happens when you over feed, If there is alot of fish waste in the pond, or to much light.
Goldfish,
Koi,platies,swordtails, mollies are really big waste producers. These fish should only be put in over the late spring or summer taken out when the weather gets colder in the fall or winter time in your area. I do a 20-25% water change each week and this keeps the Nirates,Nirites and Ammonia down which also keeps the algae under control. You can always buy some night blooming water lilies to cover the surface of the water to shade it. This is good if you have your pond in a shaded area. Plant trees, plants around your pond if it is in the ground or provide a umbrella over the pond on the hottest time of day to shade it. If it is a tub pond you can have other plants in pots around the pond this providing some shade also.
I'm surprised that the UV is not controling the algae because that is what people use to control it in most ponds, water containers at ranches that have horses and fountains without chemicals. It could be broken. The only think with UV is that it can be expensive as the UV bulb is not cheap and only last about 6 month to a year. If your pond is overstocked with way to many fish, or snails that could be your big problem also. Try to rehome the excess on craigslist or take them to the water department so that they can give them to over people for their water fountains or ponds.I asked mine and they told me they would take any excess babies I have when I got Mosqito fish last year from them.
Also Water Hyacinths are excellent in controling Nirates,Nirites, and ammonia in the water as some sewage plants use these as they work so well I read in my Tropical Fish Hobbyist Magazine on unfiltered tub ponds.
Cleaning a pond completely by scrubbing takes all the good bateria out of the pond and this can also lead to algae bloom as you would never clean aquarium filter and whole tank completely as the cycle will have to start again and this leads to problems with fish and water qty. issues. Always get a filter that rate higher then what you have if you are using a filter system in you outside pond, Bio sponge filters are the best. Never fully rinse a bio filter sponge just light rinse it to save the good bacteria in it. Unfiltered tub ponds use water hyacinth and a pond plants like water lilies, to provide extra shade to keep algae bloom down.
#1 Algae problems listed below:
Over feeding
To many fish or snails inside provoiding to much waste ( remove the excess fish or snails)
Dead plant waste, leaves ect. (use net to remove)
Not doing 20-25% water change once a week
Over cleaning pond this removing good bateria in pond ( will need to cycle again)
In a to sunny hot location ( move to area with less sun if you can or provide shade with water plants or umbrella or shade cloth above the pond area.
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