Im no Dr here but I think this cream is mainly oil based so should probably be ok if you wait a few hours before diving into your tanks, here is some info:
Locoid Lipocream contains hydrocortisone butyrate, a non-fluorinated hydrocortisone ester [Pregn-4-ene-3, 20-dione, 11, 21-dihydroxy-17- [(1-oxobutyl) oxy (11β)-] for topical dermatologic use.
Chemically, hydrocortisone butyrate is C25H36O6. It has the following structural formula:
C25H36O6
Hydrocortisone butyrate is a white to practically white powder with a molecular weight of 432.56. It is practically insoluble in water, slightly soluble in ether, soluble in methanol, in alcohol, and in acetone, and freely soluble in chloroform.
Each gram of Locoid Lipocream contains 1 mg hydrocortisone butyrate in a hydrophilic base consisting of cetostearyl alcohol, ceteth-20, mineral oil, white petrolatum, citric acid, sodium citrate, propylparaben and butylparaben (preservatives) and water.