I forgot to switch on electrics for a day and a half and my established aquarium of 48 USg became toxic with ammonia. After a day or two of fish dieing I fololishly cleaned the filter trying to rid the disease (velvet, white spot) and inadvertently wiped out all bacteria. Now I am struggling with twice daily water changes and ammonia levels of 1mg/L when in the past it was 0. The disease/stress/toxins has killed a few fish, 5 so far.
I was thinking there should be an "aquarium management" system that would (a) monitor and alarm and (b) control the parameters. An arduino with a GSM module would be able to send SMS texts with frequent updates for example. Or a web page to provide more info and control.
But ammonia and nitrogen compounds in general are hard to measure and they are the most lethal. Of course we can measure temp, water pump operation, water levels, lights.
Well it sounds like you have a lot of fish in there ( tropicals ?) and if you are still getting a lot of ammonia then you may have some dead fish still hidden in there ? would also suggest you get an in tank Ammonia remover from your lfs, there are types for either fresh or salt water use.
Something to help renew the bacteria into the tank might also help along with the continued water changes.
Assume you are dechlorinating treating / filtering the tap water ?
As for management systems, yes there are lots around, the ready made Apex system is considered the current leader though you are looking at £500 Plus. - mind it does almost everything, pc connectivity etc.
You can find plans for your own controller, I built my own a long thing ago, and it has an alarm so if the temp drops it will sound.
However I have two projects almost completed, one is a battery backed up SMS device which the pictures show, so alerting you when away.
Also doing a simple sounder temperature alarm for someone who like you forgot to turn on his main pump after cleaning and also nearly lost his tank.
Both Ardunio based