Macroalgae -> Fertilizer Trials

[elouicious]

Hey All-

I wanted to use this thread to document another hair brained idea- turning the excess macroalgae from my coral reef fish tank into a "seaweed" fertilizer. I do not recommend this for people to try- I am concerned about the salt levels and very likely will kill some plants before dialing this in, but currently this is a waste product for me that I would like to try to recycle back into my system rather than throwing away.

I have a 110 gallon reef that is a split style tank with the bottom functioning primarily as a refugium for said macroalgae and various invertebrates. Here is the main farming patch right now-







The known species are

• Chaetomorpha spp.
• Caulerpa spp.
• Halymenea spp.

And there are a few unknown/hitchhiker species. In the long term I may incorporate asterina starfish and other pest aquatic species into the mix as well.

For now I only had an overgrowth of the Caulerpa and so I trimmed some, washed it, and have placed it in the sun to dry.



I will then powder it and apply in small quantities to test plants that I have a multitude of the species.

[pagnr]

The seasalt minerals in the algae are beneficial. The excess seasalt on the outside of the plant is possibly a problem. I believe it is washed off kelp before it is processed into plant fertiliser.

[elouicious]

This was one of my questions-

I thoroughly rinsed the outside to remove those salts, but they themselves have a lot of internal water-

presumably this is maintained at ion concentrations the plant can handle but when you dry them those concentrations will go up-

The Caulerpa is crispy after 1 day in the sun

[JCorte]

Here is an interview from a few years ago with Spot Oliver from Exotica Fruit Nursery.  He shares his experience of a seven year project using saltwater aquarium waste from propagating coral reefs to fertilzer tropical fruit trees.  He's had success with it.
https://www.youtube.com/watch?v=b75rjAsvEdM

Good luck with your project!

Janet

[elouicious]

Janet!

Always coming in with the best resources- I am still going through that edible leaves book

This is some great inspiration!

thank you

[elouicious]

They were frustratingly light on the details there!

interesting about the foliar and watering applications- the point around pH makes with the standard for aquariums being around 8 but I never thought of acidifying it

It also seems like they may mainly be talking about mangoes, which IIRC, are a pretty salt tolerant species.

here is a pic of the Caulerpa after a day in the sun

[pagnr]

Seaweed has been used as a fertiliser in many regions where it is easily available.
On some of the British Channel Islands it was a big part of the fertiliser use, possibly with sheep manure. Not sure they had much else on those remote islands.
As you are probably diluting your seaweed harvest for spraying or applying small amounts of powder to soil or pots,
the amount of extra Sodium you actually apply is probably quite low.
You may want to watch out for doubling up the Sodium from other sources, ie your water supply, recycled grey water containing some detergents/soaps, water conditioners.
Otherwise unless you are going crazy, it should be ok.
Any thoughts on the actual Aquarium water, it contains fish wastes.
If you dilute it with fresh, the salt will drop.
I use our freshwater Aquarium water on pot plants when the water is changed.

[tru]

What would happen if you poured the changed water into the compost pile as a microorganism boost? Would that be worth it, or would you be wasting nutrient water that growing plants should be receiving instead?

My gut says it'd be fantastic, but really I have no idea

[pagnr]

With composting you are feeding microbes to break down organic matter.
I'm sure the fish tank change water would be of benefit to the compost microbes, but maybe more beneficial direct to plants.

[elouicious]

So I tried once with a 1:10 dilution reef water on an Inga-

Killed it and it was a large tree

I am very hesitant to use the water except on maybe some coastal species or salt lovers

Even with the dried seaweed I shook off some salt today and will probably rinse again before application

[JCorte]

Maybe start with feeding lettuce and greens so you don't risk any of your important plants. 

Dilution rate of 1:10 seems high.  There are lots of articles on using ocean water as fertilizer, with recommended use of 3oz to gallon of water or 1:30 dilution rates for example.  I tend to use any amendments in very weak solution more frequently, maybe 1 cup to 15 gallons.

I use to collect seaweed regularly for my garden in the early years, and my kids would bring some back when they went to the beach.  I would rinse them and add them to my compost tumblers. 

Janet

[elouicious]

I agree 1:10 was way too high-

for future trials I was thinking 1:100 but then the amount that I use will end up being very small.

I don't actually do this because the refugium cleans things a lot but theoretically I would be swapping out 10 gallons of saltwater monthly

[JCorte]

Once you get your dilution rates worked out, you could always guerilla fertilize trees in public places.  Just need one gallon jugs when you go out. 

Janet