I have been reading about the use of methylene blue to protect eggs. When can I put the blue in my tank? Can I use every kind of blue?
What you have been reading is correct. Fungi are a big thread for eggs, they can destroy your entire egg population. You can avoid this by putting methylene blue in your tank. If you use methylene blue to control fungi: the best is you put it in before you have an fungal infection(prophylaxis)! You can put the blue in the water first so you can stir well and the blue is well spread in the whole tank.
Next you put the eggs in the tank. Be careful what methylene you use. It has to be pure, without any trace of metal (zinc free!!!) It should be a very thin powder (like dust) and not contain any larger particles (easy to dissolve)! The methylene blue from Fish Improve has a high quality and very suitable for this use. Note: fish infected with fungi ( ex. Saprolegnia infection) can be put in red salt for three weeks ( conc: 3gram / liter) after you taken the fungi from the fish.