Silver dollar swimming oddly

Sick silver dollar, I've had the dollars over 6 months and one of them is swimming erratically today, The sub and root that are in the tank were only put in yesterday, I know dollars are easily spooked but i dont think this is the reason this fish is swimming this way(but i may be wrong). After googling i am still no wiser some say swim bladder some say food congestion, I am at a loss as what to do apart from the obvious water checks which turn out fine. Can anyone help? The tank is a Juwel Trigon 190(litres)