One huge difference between garlic and ginger is that garlic is known to have antiparasitic, antiviral, anti-fungal and antibacterial activity. This has been established as scientific fact. This does not mean that garlic has been demonstrated to cure ich. As far as I know ginger has none of these.
I hestitated to jump because I don't want to become a target. But with a quick search on the Internet I did find this interesting bit of information about ginger on the website of the Massachusetts College of Pharmacy and Health Sciences. I am still very skeptical about a ginger treatment for ich. But this is interesting at any rate. Here are two snippets and a link to the article.
<snip>
The active ingredients in ginger are thought to reside in its volatile oils, which comprise
approximately 1-3% of its weight10. The major active ingredients in ginger oil are the
sesquiterpenes: bisapolene, zingiberene, and zingiberol11,12. The concentrations of active
ingredients vary with growing conditions. Gingerââ"šÂ¬Ã¢"žÂ¢s active ingredients have a variety of
physiologic effects. For example, the gingerols have analgesic, sedative, antipyretic and
antibacterial effects in vitro and in animals13,14.
<endsnip>
<snip>
Ginger: Potential Clinical Benefits
1. Cardiovascular: Cardiotonic, antilipemic
2. Pulmonary: none
3. Renal and electrolyte balance: none
4 Gastrointestinal/hepatic: Antinausea/antiemetic, carminative and antiulcer
5. Neuropsychiatric: See Immune modulation: anti-inflammatory for headache
6. Endocrine: Hypoglycemic
7. Hematologic: Antiplatelet
8. Rheumatologic: See Immune modulation: Anti-inflammatory for arthritis
9. Reproductive: none
10. Immune modulation: Anti-inflammatory for arthritis and headache
11. Antimicrobial: Antiviral, antibacterial, antifungal
12. Antineoplastic: Antineoplastic
13. Antioxidant: Antioxidant
14. Skin and mucus membranes: none
15. Other/miscellaneous: Warming/diaphoretic
<endsnip>
Full article
http://www.mcp.edu/herbal/ginger/ginger.pdf