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Hi all, just wants to share with anyone who is interested because I couldn't find much resources about this specific set up. Been running a tank of purely marrimo and opae ula shrimp for 9 months. No filter, no pump. Only feeding spirulina and pellets every few days, and topping up of RO water every time the water goes down about 5mm.

Opae ula are thriving. They went into 3 breeding cycles where my opae ula went from 15 to maybe close to a hundred now. They have stopped breeding probably due to the tank population limit.

Goal of my experiment was to see if the marrimo was sufficient to generate enough oxygen and remove nitrates and nitrites from the water. It seems like its fine.

Wow that sure looks a great setup you have! Yeah Marimo seem to do fine in Opae ula tanks, it’s just some Opae ula websites and forums state they won’t work so they can sell their more expensive products unfortunately.

Keep us all updated on your Marimo journey! :)


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That doesn’t look like marimo balls to me. It looks like a type of algae that I get on my rocks.

Huh, should Marimo be fine to drop into a Opae Ula setup? I'm curious to try.
Any special requirements, slow acclimation?

I’d just give it a go

I have this algae covering my rocks that looks similar to OP's.

Whoops super late reply!

I peeled my marrimo balls open and flattened them because I wanted more of a carpeting aesthetic, that's why they didn't look like balls.

However suddenly now after 2 years, my marrimos are dying. Some are turning white at the tips, and others are browning. Strangely, there is also this random sprout of algae (it has happened twice) sprouting out from the marrimos. I have no idea what they are. Feels like Chaeto, buy much thinner than the chaeto I used to have. Brittle and hard. Its weird though, this tank never had chaeto, and the only thing ever added to this tank in the past 2 years is RO bottled water and food pellets. Where did this chaeto come from? Is it even chaeto?

Tank conditions is still good though, I still have berrying females, and larvae turning to juvies.

Javik wrote:Huh, should Marimo be fine to drop into a Opae Ula setup? I'm curious to try.
Any special requirements, slow acclimation?

I acclimated my marrimos by slowly increasing the salinity of my tank while I was waiting for it to cycle.

ndrewtan wrote: ↑29 Mar 2023 10:15 Whoops super late reply!

I peeled my marrimo balls open and flattened them because I wanted more of a carpeting aesthetic, that's why they didn't look like balls.

However suddenly now after 2 years, my marrimos are dying. Some are turning white at the tips, and others are browning. Strangely, there is also this random sprout of algae (it has happened twice) sprouting out from the marrimos. I have no idea what they are. Feels like Chaeto, buy much thinner than the chaeto I used to have. Brittle and hard. Its weird though, this tank never had chaeto, and the only thing ever added to this tank in the past 2 years is RO bottled water and food pellets. Where did this chaeto come from? Is it even chaeto?

Tank conditions is still good though, I still have berrying females, and larvae turning to juvies.

Hello ndrewtan,

Just want to check where do you buy your bottled RO water?

I had been topping up my tank with the distilled water and it seems to have stopped the breeding.

Thanks in advance!

Most fish stores sell RO water, failing that you can buy an RO filter and produce your own.


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