Doing Water Change- Need Help ASAP

[Jaws]

Thanks guys. I was moreso worried about the oily film on the top of the water. I haven't seen this before and though something might have got into the water and contaminated it. I added some alk and Ca buffer and did the water change anyways. I expected some corals to slime up and the skimmer to go nuts if there was a problem but everything seemed fine. Still nothing detectable the next morning but I'll keep an eye on it and post if I notice anything. Thanks for your help.

[i have crabs]

i seem to always have some film on top of the water when i mix up a batch,it seems a lot worse with some brands of salt,ive never worried about it much and i dont think its caused any trouble.

[Quagmire]

Maybe test your nitrite/nitrate/ammonia to see if anything is breaking down.