Almost always a dwarf shrimp (whether you are talking Ghost Shrimp, Red Cherry Shrimp, etc.) that turns a dark opaque white and stays that way is dying. It may die tomorrow; it may die in a week, it may die in several weeks. But once they turn that deep opaque, it is over. It's like a person having a diagnosis of some form of incurable cancer; they might hang on for quite a while, but there is no "getting better."
This is different from the slight milkiness that others have mentioned, of a shrimp about to molt. Some do this more than others. Many ghost shrimp I've kept do not have the faintest hint of milkiness, even at molting times.
A few other general thoughts about things brought up in this thread:
- Yes, shrimp require calcium. If you have relatively hard water and you are good about doing water changes, that should provide them with all they need. Feeding with a calcium-enriched food maybe once a week (like Hikari Crab Cuisine) certainly won't hurt and could be helpful in this regard, especially if your water isn't all that hard. Fresh, blanched spinach also is high in calcium.
- The trace levels of iodine found in tap water is more than sufficient for dwarf shrimp. I've kept & bred multiple species of shrimp for 7+ years now, and chat regularly with some of the top shrimpbreeders in the entire USA, and none of us have ever dosed iodine, in any amount, in any of our tanks. If you are using 100% distilled or RO water then maybe there would be need for iodine supplementation, but everyone I know who uses pure RO water adds mineral salts/buffers of some sort to the water after it comes out of the RO system and that provides whatever traces of iodine are needed. While small amounts of iodine probably won't hurt anything, keep in mind iodine is an antiseptic and overdosing it could cause problems with the bacteria of your biofilter as well as with the natural biofilm in the tank that makes up the major part of the shrimps' diet. If your shrimp aren't doing well there are probably 8,000 potential causes I would identify as being more likely to be the explanation than iodine deficiency.
- While there are several species of shrimp sometimes sold in pet stores as Ghost Shrimp (or Glass Shrimp), by far the most common, Palaemonetes paludosus, is a pure freshwater shrimp that does not require brackish conditions even for breeding. However, the young have a larval stage where they require large amounts of micro-food in the water column and typically they do not find sufficient quantities of it in an average aquarium, and so they die within a few days of hatching. Very old established tanks, especially ones that are heavily planted with lots of decaying plant matter, mulm, etc. might support enough of such microscopic life to keep the larval shrimps alive until they metamorphasize into their usual "walking" form, where they can crawl on the substrate and plants and find food like the adults do. This is a different issue from, say, Amano Shrimp (Caridina multidentata, another popular shrimp in the hobby), where the larvae require brackish-to-full-strength-saltwater to survive the larval stage.
- When shrimp molt, leave their shells in the tank. The shrimps themselves, as well as snails (if you have them), will eventually eat them to re-absorb the calcium that is in them.
- Nitrates of 40 ppm are high for shrimp--though Ghost Shrimp are perhaps a bit more tolerant of higher nitrates than other species. I know with RCS and similar species, at nitrate levels of 20 ppm I begin seeing an impact on the shrimp especially in terms of breeding (frequency & survival rate of the baby shrimplets). People I know who keep some of the more sensitive species (Crystal Red Shrimp, Tigers, etc.) often start seeing negative effects as low as 10 ppm.
Hope that helps some. Enjoy your shrimp!
