I'm not sure that you need to test for anything necessarily, as long as your tank is fully cycled. The only suggestions I can make are to be sure that you have a food source for them (enough algae or a supplemental source) and also to acclimate them slowly (I drip acclimate mine). That is all I do, and I've never had one die...
Definitely a cycled tank and food source. My Ottos have been doing well after about 2 months. They love cleaning the live plants and glass on the sides of the tank. I supplement with algae wafers that they like also. The wafers are also a source of food for my Pleco and Rabauti Corys.
As mentioned above with cycling and food source. I think the first step for getting them to survive is getting a good source, or at the least making sure they have been at the LFS for close to a week so that the stressed ones can be weaned out. When you do get some be sure to slowly drip acclimate them and keep them in the dark so they don't become too stressed.
Go for it and you will love them in return. Don't be surprised if some don't make it, its all in the distributor for the most part.
I think the first step for getting them to survive is getting a good source, or at the least making sure they have been at the LFS for close to a week so that the stressed ones can be weaned out..
This is important too. Petsmart/Petco don't really have the setup to keep otos happy. We don't have any LFS in my area, so I don't have any choice but to shop there. The Petsmart down the road doesn't clean the glass in their Oto tank in an effort to give them a food source, I don't know how well it works. I waited until the day before the new shipment came in to get my group and they all survived and are doing well. If you're buying from a local store instead of a chain, they may be able to take better care of the otos from the moment they arrive...
I bought 3 more this time to replace the 5 that died that a long time ago all where bought from Petsmart. The prior group may have died from starvation, I never really saw them around.
The current 3 I have have fat bellies, the only thing I notice is the upgraded lighting grows patches green algae on the glass where as before I just had brown algae and lower lightning. It probalby grows back faster than they can eat it in a 55G.
When you buy them look for otos with a rounded belly. If you can't see that ask when they are feeding their fish and return then to see which fish eat and make sure you get them or at least one of them that eats.
Otos are strange. But if you have one older oto in your tank and you get new ones they tend to do better then if you introduce a group of new otos on their own. It seems that the resident oto tells the others what is good to eat. If there is not enough algae in the tank (the natural food for them) then it may take a resident otos to tell them zucchini is ok.