From the filter you are using and the size of tank I would guess you have an Elite Style 95 set up, yes? I have one for my baby bristlenose plecs.
Although the label on the tank says 95 or 97 litres by the time you add gravel and the filter and the heater and decoration and the fact you don't actually fill completely to the top, you're down to 80 litres or less. With 30 fish I would suggest you are considerably overstocked, especially in an immature tank. What kind of fish are they? Fish like platys and mollies are poop machines so that will also be adding a lot to your bio load. You also need to consider fully grown size, they may only be 1 inch now but most fish grow, for example some of my cardinals are twice the size of others (a year younger)
Also the elite filter is not much good you need to add another especially if you want to stock at that level. I have a fluval 4 plus in mine. You mustn't remove the elite filter until you've cycled a new filter so you should run them side by side. Perosnally I would keep the elite filter and add a fluval u3 and keep 2 filters going permanently, then if one fails you don't have a disaster.
Are you always conditioning the water before you put it in the tank? One mistake at the level of water changes you are doing could completely kill off your good bacteria. I would suggest your tank isn't cycled that's why you're only seeing ammonia, your nitrite spike will come later.
You may not be able to do this but I would suggest you get someone to take your fish and you should recycle your tank, if you can't do that you should seriously consider reducing your stock and keep up with the testing and daily water changes. No level of ammonia is safe so even every other day is not enough.
Are you using liquid tests or sticks? Sticks are very innaccurate.