Lets try some more accurate facts regarding Ich. Rather than write is all myself, I will copy paste from reputable sources.
From a paper discussing all of the current treatments that have been tried for ich and the dosages and the results.
REVIEW ARTICLE
An assessment of the use of drug and non-drug interventions in the treatment of Ichthyophthirius multifiliis Fouquet, 1876, a protozoan parasite of freshwater fish
S. M. PICÓN-CAMACHO1*, M. MARCOS-LOPEZ2, J. E. BRON1 and A. P. SHINN1
1 Institute of Aquaculture, University of Stirling, FK9 4LA Stirling, UK
2 Marine Laboratory, 375 Victoria Rd, AB11 9DB Aberdeen, UK
(Received 17 June 2011; revised 12 September 2011; accepted 16 September 2011; first published online 14 November 2011)
It has a direct life cycle, which is temperature dependent such that the warmer the water temperature the faster the life cycle completes. The life cycle involves 4 different stages: (1) the trophont, which resides within the surface epithelium of gills, fins and other body surfaces; (2) the protomont, a free-swimming stage
that exits the fish and settles on the substrate to become the encysted tomocyst stage (3) which in turn repeatedly divides by binary fission to produce tomites which are released to the water column. Tomites differentiate into the infective stage (4) the theront, which needs to find a host within a short window to successfully complete the life cycle by penetrating the epidermis and developing into the trophont stage before it dies (Lom and Dyková, 1992; Matthews, 2005). Theronts can survive for up to 92 h at low water temperatures; their survival being inversely proportional to the ambient water temperature (Wagner, 1960; Aihua and Buchmann, 2001).
Re treating Ich- this one applies to aquariums.
long (e.g. 7–15 days in pond culture) duration in-bath treatments which target the free-swimming stages of the parasite (i.e. protomonts and theronts). Of the other two stages, the trophont is protected lying underneath the host surface epithelium (Post and Vesely, 1983) whilst the tomocyst is protected by a resistant coat (Ewing et al. 1983) and as such, are rarely susceptible to treatment.
The reasons treatment takes between 7 and 15 days is that water temperature matters and one needs to have the meds working duting the proper stages.
The above explains why we turn up the temperature. The higher that is possible, the better. However, different fish have different tolerances for maximum temperature. The nature of what we add to treat the ich also matters. Salt must be in a high enough concentration to be effective. AS with heat, tolerance for salinity also varies in different species of FW fish. Similarly some meds work faster than others. The standard chemical treatment is a mix of malachite green and formaldehyde. However, this was outlawed many years ago for use with fish intended for human consumption. However, it is permitted for out ornamental fish.
As a result of the above there have been a large number of other drug, chemical and natural treatments tried for Ich. The study from which I quoted has more information on a variety of ich treatments including dosages how well they worked or failed to work and, if they worked, at what life stages they did so., The paper contains more information in Ich and things tried to eliminate it than most of us ever want to read.
http://dspace.stir.ac.uk/bitstream/1893/10147/1/Picon Camacho et al Parasitology Ich chemo review.pdf
Next, Tetra's Liefeguard likely will zap Ich but it is a pretty caustic treatments one may wish not to use. To decide I suggest your have a read here
https://drjohnson.com/whats-in-tetras-lifeguard-product-and-what-does-it-do/
