I think you read one of the dragon riders of Pern books by Anne McCaffrey.
From the description you give, I expect you read Dragonsdawn as it tells the story of the landing on Pern, the discovery of the fire lizards, and the first pass of thread.
"Thread" is probably the thing you called "acid."
The effects of threadscore is similar to an acid burn.
Thread also destroys large swathes of unprotected land.
At first, the colonists fight thread using flamethrowers mounted on the various flying machines they had brought with them. The periodic thread fall all over the colonised areas takes its toll on machines that should have been usable for decades - the machines start failing and the colonists look for something to replace them.
The fire lizards native to the planet instinctively fight thread - they burn it as it falls with their fiery breath.
The fire lizards are too small to protect all the settled lands, and too flighty to rely on anyway.
The colonists genetically modify some fire lizards to grow larger and be more intelligent.
The modified lizards are large enough to carry a human.
The modified lizards are called "dragons."
The combination of a fire breathing dragon and a dragonrider makes an effective replacement for a worn out flying machine.
Organized into large groups, the dragon riders can effectively defend settled areas against thread.
Entertaining stories, and there's a lot of them.
Fire lizards (and dragons) have abilities that weren't obvious, and that turn out to be quite useful - and important.