Double dose of Lasix

My 88 yr old dad was diagnosed with CHF approx. 2 yrs ago.  He has a pacemaker/defibulator.  One of his meds are Lasix 10mg daily.  He went for a checkup recently (not his regular cardiologist) and had a chest x-ray done.  Results showed some fluid.  He was told to double up on his Lasix.  What could be causing this fluid build up and is it safe to increase Lasix?  My concern is that he saw his regular cardiologist approx 1 month ago.  He told my Dad that he did hear a "girgle" when he listened with his stethascope, but never recommended that he increase his Lasix and didn't recommend a chest x-ray.  

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it's very common to double on the lasix to get rid of the fluid, caused by the heart not being able to pump well enough. the doses are probably 80-120 mg to get rid of the fluid,  the only precaution is take potassium supplements which your doctor probably recommended