Saturday, November 12, 2011

Dealing with hydrozoans.

Hydrozoans are one of the nastiest creatures that could invade your aquarium. Once they are there its very difficult to remove them. They spread very fast and may take root all over your tank.

Hydrozoans may not affect your tank negatively. Some jellyfish get along with hydrozoans. Often times, however, your jellyfish will not coexist with the hydrozoans. This means they must be removed before they overpower and kill your beloved jellyfish.

The most straightforward method of removing hydrozoans is to bleach your tank. Depending on your tank type this may be a simple task or a difficult task. Kreisel aquariums are relatively easy to bleach. Just shut off water leading to and from your sump area. Take out your jellies and anything you wish to not bleach. Then add bleach to the water. the amount depends on the size. The bleach should kill off everything in the tank. De-chlorinator should be used to neutralize the bleach. I'm currently unsure as to how much dechlor you should use, but it is proportionate to the amount of bleach you use. Now, bleaching your tank will only kill the hydrozoans in the tank and not in the full system. You would have to bleach your sump as well, which would kill off all the beneficial bacteria. If the hydrozoans become a problem then you may have to do this.

Having a smaller 9 gallon cylindrical tank may be more difficult or easier depending on how you look at it. You will pretty much have to nuke your whole tank with bleach. They hydrozoan hydroids attach themselves to the substrate and that will have to be bleached. Sadly that means getting rid of your colonies of helpful bacteria. These colonies may grow back fast since there is the same bacteria living inside your jellyfish. So just move your jellyfish and other live material (snails, crabs, fish etc) into a safe holding tank. You can just put everything in a rectangular glass tank until you finish bleaching. scoop out the marbles and then the ceramic media. Put them into two separate bowls. Trust me, keeping the two separated save you and hour or two of sorting out the marbles from the rocks later on. Add about a cup of bleach to the empty tank. As for the substrate, wash both the marbles and rocks (separately!) in a strainer with very hot tap water. The heat, chlorine, and fresh water will help kill the hydrozoans. Then you can bleach the media or boil it for an hour or so. Just make sure that ceramic rock is really soaked. It's very porous and small hydrozoans may take refuge in those pores and then return in your tank.

Once you are sure your tank and substrate media has been sterilized, you can return everything to the tank. Personally I would drain all the old water out and wash everything then get new saltwater. I feel a good wash of everything will remove dead hydrozoans and will give your tank a fresh new start.

Bleaching should leave you with a hydroid free environment, assuming you eliminated their source of entrance as well. Hydroids can come from a variety of sources and you should make sure you don't introduce new hydrozoans into your tank after you go through the suffering of bleaching your tank. These sources may include~

  • Brine shrimp eggs.
  • Hermit crabs. 
  • Ocean water that has not been sterilized.
  • Live rock/live sand.
  • Things bought from major pet shops. 
You can eliminate hydrozoans from brine shrimp eggs by getting decapsulated brine shrimp eggs. These are eggs that have been bleached to have the shell removed. Some varieties of these eggs will still hatch, and get rid of the hassle of separating the hard brine shrimp shells from the shrimp. They are also often free of hydrozoans. just make sure your supplier specifies that they are sterilized and also still hatch-able. 

Try not to buy hermit crabs or fish/ invertebrates from major pet dealers. Buy from reputable fish stores. This may help eliminate hydrozoan introduction.

If you want to use real ocean water then you should sterilize it first. Otherwise, using manmade saltwater works just fine.

Sand and live rock aren't often used in jellyfish aquariums since only certain jellyfish can tolerate sharp objects in their tank. Jellyfish art's tank uses live rock as filtration. The tank comes with dry ceramic media containing no life. They some live rock with every purchase of jellyfish. So there is no need to add any live rock which could introduce hydrozoans to your tank.


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