Doing Water Change- Need Help ASAP
 

So I'm doing a 40G water change on my 180G tank. I've had the salt mixing for a couple days now. I noticed tonight that when I went to do a water change there was a film on the top of the water. I tested the params and they're all a little low but they don't look too bad.

Ca 330
Alk 8.0
Mg 1175
Salinity 1.021

Now I was at then end of two buckets of Kent salt that I combined to make this mix. Both buckets were totally fine in previous water changes. I was about two cups short on salt which shouldn't make too big of a difference since my salinity is 1.025 in the main tank. Should I use this mix? What do you think?

I've got supplements to bring the levels up to where they should be.

I would boost the Ca, I do for all replacement water. The salt seldom contains as much Ca as the Company claims. Some Baking Soda will push the Alk up too, although it's not super low, Seawater is 8.2 I think.

Increasing salinity closer to 1.024-1.025 will somewhat increase the Mg and Ca of your salt mix. Probably will increase your alk, too.

I would adjust the mix to meet the levels of your main tank with suppliments. Starting with Mg.... then Ca and Alk. I find if you bring the Mg levels up first then the CA doesn't precipitate.

I am sure you know where your levels need to be but here are mine anyways:

MG: 1360/1400
Ca: 435
Alk: 3.45 Meq/L
Salinity: 1.024


Rich.......

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 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.

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