Tanglewood Elecroacoustic String Problems

[CypherA9]

Hey Guys,

I have a tanglewood electro acoustic bass with rotosound bronze bass 44 Phosphor Bronze Roundwound strings on it at the moment.

The problem is that once i put a new set of strings on the bass they play great, tone comes back and sounds great, but after a few days there just as bad as the old ones, they go really dull and dirty and dont sound as good .

Is this typical with all phosphor bronze strings or this brand? The strings are too expensive for me to keep replacing so is there anything i can do to help prevent this .

Any help greatly appreciated thanks guys .