It would be really great if the people that have access to natural seaweed show the process of gathering it and preparing it for your garden!
Here's what I know.
1. Do some honest research and pick your algae. Google: algae, fertilizer, horticulture, nutrient analysis etc. I like to stick with the brown algae (Phaeophyceae) Padina, Sargassum, Fucus, Macrocystis, Laminaria are all good. I like Sargassum because it has 8% potassium. Macrocystis has 33% magnesium. Padina is well known for it's Calcium. I'm currently using both Padina and Sargassum in my grow. Greens and Reds are not always the best choice nutrient wise. Greens are especially low in bloom beneficial components, but good for veg.
2. Collect as much as you need. Ten pounds of seaweed will yield about a pound of dry.
3. Bring home and split the batch, reserve about half to be blended into shakes and the rest for baking.
4. Rinse everything by dunking 3 times quickly in fresh water to remove bs external salts
5. Blend the wet portion with a small amount of water (just enough to keep the weed spinning in the blender). Pour the blended portion into your choice of containers and freeze (fill zipper bags or make ice cubes or fill dixie cups etc and freeze for later). When you want some fresh seaweed just remove the frozen stuff and reconstitute in warm water. You could also fill container and store in the refrigerator but it will not keep as long. Blended fresh wet algae is not preserved/pasteurized like the stuff that you get over the counter (lack of preservation chemicals may be a good thing, but the home made shakes won't last as long).
6. Bake the rest of the kelp at 250F until crispy and crackly (takes some time and patience and it really smells good). If you accidentally burn some that wont hurt the mineral content but it will reduce the organic content (a little bio-char never hurts). Keep in mind if you want the precious organic materials (growth hormones) in the kelp don't dry it, instead blend it and freeze it. I suggest making both liquid suspension and solid flakes. If you have access to a freeze-drying machine then do it because freeze dried algae is the best way to go. Sun-dried algae looses some minerals, oven dried algae looses some organics, freeze dried algae only looses growth hormones. Wet algae retains everything. I use a Barbeque outside to dry my algae, which cooks it fast but I probably loose a little of the organic benefit (I like my algae for the mineral content mostly, any additional organics are a plus).
7. Put the dry baked weed in a dry blender and spin it down to a powder. Use a seasoning blender or such.
8. Freeze the powder to keep it fresh.
Keep in mind the powder is about 10 times more concentrated than the liquid suspension.
1. Use the seaweed ice cubes for making teas and foliar feeding.
2. Use the powder to boost your incubating organic soil mixes
3. Use the powder as a top dressing on your soil prior to watering
4. Use the powder in you teas also.
5. I like to combine the seaweed with fish emulsion and molasses in my teas.
Basic tea instructions: 1tps each, seaweed powder, fish emulsion, molasses and incubate for 24 hours at 85F for 24 within 2L bottle with 1L water and a bubbler stone. From this concentrate make a 1/20 dilution using your feed water. Feed with the 1/20 dilution. You can replace the 1tsp powder with fresh blended algae by adding 3 tablespoons of wet blended algae to the above recipe.
Feed the plants once a week just prior to their regular watering.
You can't really go wrong with these instructions. You'll never have a CaMg deficiency if you feed with a decent algae.
I'm a soil grower so I wouldn't know how to adjust these instruction for hp/dwc. But anyone on hp/dwc should be able to figure out the dosage.
My suspicion is that MOST of the products we buy in the bottles at the store has been heavily processed and a lot of the minor beneficial components are lost in the processing. There are probably some good products out there anyhow.
Any questions send a PM.