Hydroponic style grows fascinate me but I grow in soil. I have bought coco coir bricks and blocks just to play around with the stuff to see what it is like but never have grown anything in it or in a mix of coco and something else.
But,if it is the Damping Off that you are asking about then the pH is not a concern. The thing to find out is why the fungus is still causing problems on the next seed planting session.
Maybe buy or ask someone for some quality potting or 'seed starting' soil mix. Just as an example I am thinking of something like Fox Farms Happy Frog. It is just an example and I have never used it myself. But it is frequently recommended so it must have something going for it.
Buy it at a full service gardening center or hydro or grow shop since those places often have a faster turnover than big box stores. Put those containers you have been using away for now. They are to large. Large containers when starting seeds or trying to get cuttings to root so as to get clones makes it harder to control the moisture levels and sometimes the temperatures of the soil. The 16 ounce Solo Cups are a popular choice. If that is all you have go with it, you will be in good company. When the spring rush comes and everyone is putting in flower and vegetable gardens then check the curbside trash. Look for the seedling containers that people are throwing away. Build up a stockpile for later.
Put some of the new soil mix in the small containers, put in one seed per container, water it just enough for the soil mix to be moist. I am thinking that a teaspoon to help with the watering should be sufficient. Put the small containers someplace that stays warm, but not hot. Label the containers with the usual notes like strain name and the date.
Sometimes a window sill will get very hot on a sunny day and the seedling containers will over heat. Also, the area for a couple of inches away from the window is cooler than we realize on those cold nights.
Do not water again for several days; or think of it as for a long time. That container should stay moist for 3 or 4 days, maybe 5. By then the average Marijuana seeds have sprouted so write down the date they popped up through the soil. Take care of them. Do not over-water. Do not let the surface of the soil stay wet.
If all goes well they will not have any problems with damping off. In a week or two you can then transplant to the next larger container. You can transplant back into your coco mixes, or new coco, if you want to go that route. My suggestion is to find out if you have a root rot or Damping Off problem living in the coco mix you already have.
