Question
Hello, recently I have had a small problem with mosquitos breeding inside of my water trays so I followed your advice from the ebook and bought some mosquito dunks. I placed one ring in each of the trays and within one night all the larvae were dead. I left the rings in there figuring it would help prevent more mosquitos from breeding in the trays but noticed that the traps of the new growth were turning black before forming into a grown trap. I have been using strictly rain water (TDS reading of less than 10) and distilled water. They were growing very well until I placed the dunks into the trays. I also took a reading of the water after the dunks were in the trays for 24 hours and the TDS reading was upper 100's. I can't pin point anything else that could of caused this besides the dunks. They get 8+ hours of direct sun. Should I not have used the whole ring in such a small tray? Maybe break of a quarter for each tray? Could it be that they are starting to grow "summer" leaves and the ones that died couldn't handle the summer heat that we have had recently here in Mass?

Best Regards, Ken

Answer
Hi Ken,

This is the first I've ever heard of this happening.  We've used dunks for years with no problems.  However, a whole ring for a small tray is quite a bit.  In the greenhouses during the summer I use just a quarter of one.  A whole ring is enough to treat a small pond.  I'm not sure what other ingredients the dunks have besides the bacteria.  Traps not completing formation is consistent with hard water.  If they do have some calcium carbonate in them, it wouldn't have as much effect in a large body of water.  I would say change the water and use a smaller amount of the dunks.  The heat by itself is not as likely to be the cause unless your pots are in a particular exposure that overheats the pots.  If you get a chance send me a photo of your plants and your set-up.

Good Growing!

Jeff Dallas
Sarracenia Northwest
http://www.cobraplant.com