All three of the Esterbrook Dip-Less Pens shown were inked until a few days ago. Actually, I even have a fourth, but the need for three desk pens was already pushing it.
The bottom pen is still inked, with Noodler's Walnut, in case I want a brown ink. The double set on top had Private Reserve Black Cherry (not really a red, more a rich, vaguely reddish brown) and Noodler's Black American Eel. It's now empty. I have a couple of Varsities in case I want a red or a black ink.
A couple of days ago, taking the Black Cherry pen out to write with, I notice that there was a white fuzz on the feed. Looking inside the bottle, I could see that it was there too. I've seen this referred to as SITB (slime in the bottle), a growth of mold that can happen in inks when mold spores get inside there. It was my first personal experience with this.
There was nothing in the black ink side, but because of the dual design, it seemed easiest to clean the whole thing. I emptied the inks, completely disassembled the whole thing, and soaked all the parts overnight in a bucket of water and ammonia solution. A couple of hours would probably have been fine, but there were distractions, and I forgot about it. Of course, there was some danger of the ammonia damaging the pens or the base, but I seem to have gotten away with it. After rinsing all the parts, I soaked the nib feed assemblies in a glass of ammonia solution for another couple of hours.
It's possible I will fill these again at some point, but first I want to see if I get any kind of growth on the dry pens or the base unit. The feed material and the base unit are both somewhat porous, and ammonia is not necessarily effective with porous materials.
The single Dip-Less set at the bottom of the picture is a later style where the pen does not dip directly into the bottle; the nib sits in a nest of plastic rods which draw up the ink from the bottle by capillary action. The dual set is different; the bottles are inverted and the ink gradually runs into the base unit, forming a puddle of ink that the nib dips into. I've noticed before that this seems to lead to the ink evaporating more rapidly than you'd expect. It may also have allowed airborne mold spores to settle in there.
Anyway, an interesting experience, and hopefully useful to others who may be considering the Dip-Less models. These are the Esterbrooks which I've used most often over the past two or three years, and I do like them.