Fish 'scratching' on rocks and decorations?

While Ectoparasite infestation is the most common cause of this behavior, the flashing/scratching 'could' be something else. fish can be irritated by metals such as iron, copper in the water. if this is the cause, the fish seem to 'flash' most often right after a water change and less as they 'get used' to the irritant then the cycle is repeated at each water change. Note that this reaction to metals is not the same for all fish all the time. Have your water checked for heavy metals or ask your municipal water company for analyses. This is a good place to start.

Fish can also flash in response to parasites other than the more obvious Ichthyophthirius (ich) gill flukes for example which are not obvious externally but require a more internal investigation (gill scraping and viewing under a microscope) gill flukes usually result in reddened, muccous covered gills.

Elevated levels of ammonia, nitrite or high/low/widely fluctuating diurnal shifts in pH can also cause irritation though you haven't given your water parameters yet, you will, right?

Gill flukes are a possibility these are monogenetic trematodes that need no intermediate host to reproduce. They are reasonably common aquarium pests, especially; it seems, in the cichlid aquarium. Egg-laying adults are 2 mm in length with damaging anchors and hooks. Their tough shelled eggs hatch in 1-5 days, often requiring repeated treatments to control serious infestations.

Adult fish normally tend to have a few flukes, and this minor population is considered like a few fleas on a dog mildly annoying, but not an immediate emergency. Fry and juvenile fish, however, are often devastated by a fluke infestation, and often whole broods are lost just when they have started to get a little growth on them. It is not unusual for a whole tankful of dime sized fry, for example, to suddenly start hanging at the surface and die off a handful at a time over a few days time.

The main problem with fish gills is that unlike the rest of the body, we can't readily see what is happening often by the time it becomes obvious that the fish is ill, the damage is advanced and untreatable, so therefore an early diagnosis and treatment is vital. 

The early signs are (a) fish respiring heavily you can judge this by watching the operculum movements and comparing them to other fish. (b) Fish laying on the bottom for long periods - general lethargy - not eating. (c) Fish tending to use one pectoral fin, keeping the other folded back against the body. 

At a more advanced stage you may notice that the fish can't fully close the operculum because of gill swelling. Affected fish may segregate and stay alone - often near the surface or water return. There may be strands of mucus trailing from the gills. At a really advanced stage - and usually too late for treatment - the fish will lay on the bottom with its pectoral and dorsal fins clamped to its body - literally waiting to die. Treating against parasites can be a problem in advanced cases. The combination of excess mucus and hyperplasia forms a secure shelter for any parasites between the secondary lamellae making them very difficult to get at. 

Treatment: To treat flukes, first and foremost, give the aquarium a good maintenance session with a 50% water change and attention to the substrate, filter media, and inside glass. This to me is the most important part of the therapy, and cannot be avoided. You will already have, through this act, reduced the fluke population enormously, in addition to reducing bacteria and other toxins in the water, increasing the oxygen, and preparing the water for further treatment.

Next, a salt bath is a good start. It won't exacerbate the problem and will help remove any excess mucus or parasites. The dose is four ounces of salt per ten gallons of water, maintained over three weeks to prevent reinfestation with newly-hatched flukes if the salt treatment fails to work, Formalin and commercial formalin/malachite green combinations can be used to combat gill flukes this is probably the most effective. Due to synergistic effects, formalin and malachite green together are more powerful than either is alone. Up to three treatments at weekly intervals may be required to knock down persistent fluke problems.

These treatments are a bit more challenging and require careful attention to risk and safety factors. Formalin is added to the aquarium at three drops per gallon in soft water and up to six drops per gallon in hard water for an 8-hour period followed by a 50% water change. 

Alternatively, a bath of up to 15 drops of formalin per gallon can be applied for 30 minutes but only with vigorous aeration and constant supervision. If the problem is an "ich" infestation note that this protozoan has a very complex and interesting life cycle: Mature parasites, which have been feeding on the host tissues, fall away to the bottom of the aquarium where they become enclosed in a membrane forming a cyst. At this stage they divide, each cyst producing hundreds of infective 'swarmers'. These swim throughout the tank attaching to host fish and if they don't find one within 24-48 hours they die. 

The time to complete the full life cycle (from fish through cyst and back to fish) varies with temperature -- the higher the temp the faster the cycle. Three days at 70deg. and five weeks or more at 50deg.F. 

While the parasite is attached to the host it is protected by at least one layer of tissue and possibly more and thus is immune from treatment by chemical parricides. The treatment is therefore targeted at the free-swimming stage and thus takes a considerable length of time to kill all the encysted larvae since they do not become free swimming all at once.

Various treatments include one of several proprietary anti-parasitics such as formalin alone or in combination with malachite green, copper, acriflaven, triethylene glycol and victoria green or salt bathes. 

Certain scale less fish, particularly catfish and clown loaches may be sensitive to these chemicals and should only be treated with parasites specifically formulated for them. Alternative treatment which obviates the need for chemicals of any kind is use of high temperature -- 90 deg.F for several hours a day every 3-5 days will eventually rid the tank of 'Ich'.

While most conventional medications state that they cure 'Ich' within 24-48 hours this is really not true. The white spots may disappear but the encysted stages remain for several weeks more and may re-infect weak or poorly conditioned fish.

To add salt, mix it with some of your tank water in small volumes and add to your tank. never dump salt in directly as a solid add ¼ tsp. per gallon once an hour for four hours this will bring your tank to a level of 1 tsp. per gallon in four hours then increase it to 2 tsp per gallon in ¼ teaspoon increments every 3-4 hours. always watch the fish closely for reaction. When you reach a level above 1 tsp. per gallon, watch for signs of increased stress and if noted, slow things down and allow the fish more time to adjust.

Carbon will not remove salt from the water so if you are using it you do not need to remove it as you do with meds table salt, pickling or canning salt, kosher salt are all fine to use the levels of iodide or flow agents are too minute to be a factor. 

During this treatment, increase the tank temperature to at least 82°F. note that 86°F is usually fatal to ICH, and if your fish will tolerate this temperature this alone can kill the parasite. important note ... warmer water does not carry oxygen as well as cool water. increase oxygen concentrations in your tank during treatment by (a) lowering the tank water level to increase splash, (b) raising the spray bars above the water line, or (c) add an air pump to your system with a good bubbler maintain this treatment for two weeks minimum.

You can use salt with cories, catfish, sharks, loaches, tetra’s pleco’s etc., basically any fish can tolerate the level of salt recommended for the time involved in treatment.

It's important to continue a water change regimen during treatment and recommended twice a week but remember to replace what you remove just add whatever your target level is to the change water for example, if you have 2 tsp. of salt per gallon in the tank, and you change 10 gallons of water then add 20 teaspoons to the change water as it goes back in. the total level of salt in the tank will remain the same.