My corys aren't very old at all, not full grown size yet so the spawns are small. I haven't done any water changes with colder water, in fact they spawned 3 times the last time with no water change during this period.
My opinion is that they love a lot of water flow to lay the eggs and if they don't find such a spot they won't lay eggs. I am yet to see eggs in the part of the tanks where the current is very low. My guess is yours may have spawned but the eggs may have got eaten pretty quick, in minutes or hours, if you have other fish in the tank. And the corys don't like overcrowded tanks too.
And the ammonia in the tap is a downside. They'll wait until water conditions are fine.
I used to keep mine in the 30G tank I have and although they spawned, they stopped for a period of time when I had ammonia for a day twice in the space of a month due to me washing one of the sponges of one of the filters. Whatever it is about this particular sponge, it seems that all the bacteria loves it and a brief shake in tank water causes a spike in the whole tank although there are another 2 sponges in the same filter and a second Fluval U4 in the tank. I gave up touching this sponge and it's falling appart The corys don't tolerate ammonia well at all. If you ever see them looking stunned/hiding and staying at one spot for longer periods of time then they are more than likely not happy for one reason or another.
My opinion is that they love a lot of water flow to lay the eggs and if they don't find such a spot they won't lay eggs. I am yet to see eggs in the part of the tanks where the current is very low. My guess is yours may have spawned but the eggs may have got eaten pretty quick, in minutes or hours, if you have other fish in the tank. And the corys don't like overcrowded tanks too.
And the ammonia in the tap is a downside. They'll wait until water conditions are fine.
I used to keep mine in the 30G tank I have and although they spawned, they stopped for a period of time when I had ammonia for a day twice in the space of a month due to me washing one of the sponges of one of the filters. Whatever it is about this particular sponge, it seems that all the bacteria loves it and a brief shake in tank water causes a spike in the whole tank although there are another 2 sponges in the same filter and a second Fluval U4 in the tank. I gave up touching this sponge and it's falling appart The corys don't tolerate ammonia well at all. If you ever see them looking stunned/hiding and staying at one spot for longer periods of time then they are more than likely not happy for one reason or another.