How do I know if there is too much algae in an outdoor fish pond or pot?

Question

This question Would my fish benefit from snails in their pot pond? asks about having snails in a fish pond/pot to reduce algae.

My fish are happily living in a outdoor ceramic pots, approx 80cm high x 50 cm in diameter. They have fish pond mud, sand and aquatic plants. The walls have algae, which is hard to see, unless the sun is shining through one of the pots in the morning, as the pots are painted black (on the outside).

I am concerned that the coming summer may mean an increase in algae and am wondering how this will affect my fish and if there are signs I should look for, both within the environment and the fish to see if algae is at an unhealthy level?

Answer 1

If I've done my math right, those pots will probably hold a bit under 40 gallons of water (depending on the exact shape of the pot, depth of the substrate, etc.). That should be sufficient for two or three adult goldfish assuming adequate filtration. I would have concerns about temperature fluctuations given the black paint job in the sun though.

As far as the algae goes, I know you already have some plants, but adding some floating plants might help to keep the water clear. Water hyacinth and/or water lettuce would probably be good candidates (as long as your goldfish don't snack on them too much).

Adding a few snails or a compatible fish that enjoys a high algae diet may also help. Bristlenose plecos are generally considered to be fairly goldfish compatible. They tend to stick mostly to eating algae and driftwood, and don't snack on slime coats like some other plecos will. They get large enough not to be eaten by the goldfish, but stay small enough that you should be able to get away with one in a 40 gallon tank/pot. They will also tolerate the cooler temperatures that goldfish prefer. Just be careful not to go too cold! (72-77F is generally best for them.)