I'm new here, so, yeah. Anyway, I have just ev trained a Kingdra so it had 252 HP EVs (to level 50). Its HP was only 181, whereas it should have been 182. Also, its HP IV is 25. Please help! I don't know what's wrong!
What level before EV training did you check it on Serebii? If you checked it after then your IV calculation is off somehow. The lower the level you calculated IVs the more innacurate they will be, but usually they will give you a range. Also, you could have messed up EVs by accidentally battling the wrong Pokemon once or twice.
Possibly, if you put the Kingdra into your box, and take it out again, its stats should adjust to their proper values. Depositing Pokemon in the box will put their stats at what they should be, taking into account IVs.