Had my first major tank crisis this past weekend. It was a crisis that could have been avoided if I had only not been so derelict in ordering a backup return pump. I have quite a few pumps, but because I hard plumbed the system with a Jebao DC pump which has a 1.5" inlet and 1" outlet, none of the available pumps - (2) Bluelines and a few misc, Tunze and Eheim - would work as a substitute. So I was forced to utilize the Waveline I have powering the skimmer. However that too didn't have the same sized connections to the Jabeo, so I rigged it with flex hose, hopiing it would suffice until today when the replacements were to arrive.
What I didn't realize is that because the skimmer pump was drawing water from near the overflow from the tank to the sump, a few things were to begin to occur. The first was heat buildup as there was no real movement thru the sump and thus very little evaporation. I effectively short-cycled the system. The next was the remaining water in the sump becoming toxic with ammonia because of the lack of circulation. This was all exacerbated by the fact that the skimmer was also off-line, not providing nutrient export or aeration. The tank still had internal flow - two MP40 and two Tunze 6105, but they do nothing for the heat which was created by the Waveline shortcycling the system flow and in fact, being internal, the Tunze were adding to the heat buildup.
So last night I was up until 3am rigging the Waveline pump to work with the flow of the sump and changing out the 30+ gallons of water the sump holds. This all could have been averted were I to have just ordered a backup instead of having kept telling myself - I need to order a backup

I knew this was a possibility, yet I was just lazy about ordering it when I was thinking about it.
Fortunately there were no losses even though the tank temps reached 88+. Thankfully a replacement arrived this morning and I will be putting things back the way they were. I'll also be re-plumbing the system. Though I ordered another Jabeo to expedite things since it's the holidays and time is at a premium, the Jebao lasted just a year and then crapped out for no reason. I'll probably purchase a few Askoll pumps and re-plumb everything to work with them. They're rather inexpensive and pretty dependable with good flow. I prefer external and something quiet, which I think these are.
So take a lesson from my mistake and have at least one backup return pump on hand. I always did - that's why I have two Blueline 55 LOL, but for some unknown reason I didn't think to have one to replace the Jabeo.