As the title suggests, you should really keep a large amount of pre-mixed, at temp salt water stored, as well as a supply kit of chemical/metal scavanging media like Poly-Filters, carbon, cuprisorb, etc.
Because eventually your tank will try to self destruct.
I won't bore you with the blow-by-blow description... let's just say that when a Koralia Nano powerhead's internally potted components are not sealed water-tight, very bad things happen.
Saturday evening, I noticed my ORP levels were really really low. I cleaned off the probe tip which didn't do anything, and just chalked it up to a bad probe. Everything looked fine and all fish were accounted for so I just went to bed.
Sunday morning, all did NOT look fine - all LPS
corals had their mouths gaping open, spewing out mesentary filaments and coating themselves with mucous. SPS
corals were not looking good. Mushroom and sansibia were closed up tighter than tight. Fish were all OK, though.
After searching for some obvious culprit, I found the Koralia Nano I have on my back glass was spewing a column of hot water from where the cord goes into it. Y'know how the water column around your heater looks distorted when the heater is on? That's what I was seeing coming out of the BACK of the Koralia. It wasn't ejecting anything that I could see... just the hot water, but obviously it was doing more than that. (Tank temp was normal.) No stray voltage in the tank, but it was obviously putting something chemically bad into my tank.
So I yank that powerhead out of the water, and it was h-o-t... really hot. Throw the thing downstairs and move on to water changes.
I normally keep 20g of salt water at temperature, stored, for just this reason. (My tank is a 46g) But I've been lazy over the last couple weeks. I only had 8 gallons stored. Grrr.
So I do an 8g change Sunday morning and put a bunch of Poly-Filter pads in my HOB
equipment, as well as a bunch of carbon. (Poly-Filters will suck bad things out of your water like ammonia, copper, etc... and are really good things to have around.) Things start to perk up a little. I immediately start mixing more water and do a 12g change about 12 hours later on Sunday night. Things looking even better.
So the moral of the story...
1. Always - ALWAYS - keep salt water stored, at temperature, ready to use at a moments notice. Eventually, if you stick with the hobby long enough, you will *have* to use it.
2. Also... keep on hand media that can suck nasties out of water, as well as a plan on where to put it.
And although I'm still ticked off at myself for not trusting that ORP reading and looking for the culprit Saturday night, I feel I got off lucky. It's still too early to tell, but I think I only lost two corals, a Seriatopora and a Lithophyllon. My Turbinaria, Stylophora, and Duncan still look pretty ticked off, but I'm crossing my fingers they'll make it. Everything else appears to be returning to normal. Several snails appear dead, but amazingly my cleaner shrimp is still alive.
So hopefully my little adventure this weekend will make some others think about their own "emergency plan" and adjust if required. Still not sure what happened with that powerhead - could've just had a manufacturing defect to start with. But I think I'm going to start replacing them every 12-18 months or so... just to be safe.