Now, i have come up with some ideas.
For the over all control i think you will need something like an axon, but i don't know if that will work. Something along those lines, a mother board.
To feed the fish you can use a revolving chamber (presentation 1). Peice 1 sits in side themain body. between every gap sits the food for a meal. If you click on the feed button the servo will move around 1 space dumping in the meals food.
To watch the fish you can either write some code and attach a usb port to the mother board to accept a web cam or you can get a black fin or eqivelant for easy use, but they cost lots so i would spend the extra time on the Web cam idea.
To measure the temperature all you need to do is get an old fashion mercury thermometer and place it in the feild of view so you can see it when you watch the fish or else you can get a digital thermometer and plug it into the mother board.
For the pH i guess you might need a digital meter that you can plug into the mother board.
To add chemicals you might be able to make a mechenism like the food supplier toadd the needed chemicals.
And if you want to you may be able to make an external unit for adding food and chemicals.
To turn in the tank lights all you wald have to do is add a digital switch to your board and the lines of the power source. The only problem may be the voltage if you want the power straight from the wall. You can always get a timer from the hardware store that will turn on and off the same time day and night.
If you want to operate it throught the internet though it is gonna need its own software and is gonna take a tone of programming if you do it your self. You might be able to find a commercial program that yiu can get of the shelf.
I will do some further research