To whiten my washcloths, I use a goodly amount of liquid bleach and liquid laundry soap -- I put the cloths in while the tub is filling, punch them down into the water, and let them soak 5-10 minutes. Let 'em go through the wash and rinse cycles, then put 'em through the wash and rinse cycles again with only clear water both cycles.
Try soaking in vinegar and water solution. You probably have hard water. You may want to consider having a water softener installed.
You can buy bluing in the laundry section of the store. It comes in a small bottle and will last for a long time, as you only use a few drops per washer-load. Just put it in the rince cycle. It really helps dingy whites or water-stained whites look much whiter. (Don't use TOO much or you end up with Blues instead of Whites, LOL) You might also try putting a cup of OxyClean in the wash cycle... that stuff really works, too... it took grass-stains, caked mud, etc. off my son't white football uniform pants. Hope it helps!
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