You can still treat for hydroids - either before or after you get the dwarves - but if you wait until you see the little @&#&@ it may be too late to save them. Here is info I recently posted about hydroids:
Hydroids come in a few varieties. There are the tiny jellyfish looking ones.. when swimming they appear to be jellyfish and when on the glass they are described as dots with legs.. a center dot with 8 or 9 tentacle dots in a circle. There are the cobweb looking ones... usually attached to the glass or objects in the tank but sometimes freefloating - these are very fine strands. I've also heard of a "pink fuzzy stuff" type but I have never seen these.
Panacur is actually sold as a dewormer for pets or livestock. I've bought from this place:
www.kvvet.com
You want the Panacur Granules 22.2% - the dosage is 1/32 of a teaspoon per 10 gallons - treat 3 days in a row with a 25% water change before each new dose. What I did was set up the tank and cycled it, added everything I wanted in it then dosed the 3 days with the last day being the day I added the dwarfs - since my broodstock was to be wildcaught and they often bring the hydroids with them. You can treat with the dwarves in the tank. Panacur will not harm the biofilter, fish, macros, pods, or shrimp. Panacur will kill some types of snails (particularly astrea), fans, worms of any kind, most if not all soft corals, gorgonians, all stars, etc. The effect on these creatures can last over a year.
There is a lot of hydroid/panacur information at seahorse.org - a search there will give you all the known details.
Also, if you start with 4 in a 1 gallon tank, be ready to expand - 4 is about max for that tank. My 11 adults had 27 fry the day I got them (2 broods) and before I had them 4 months I had a total of 63 dwarves - and at least 2 are pregnant now.