Advice on rebooting high phosphate tank

[Joseph_Joe]

Hi all,

I would like to get your advice about rebooting or not a tank.
Mine is 50g that is 1.5 yr old.
I started it with dead rock that I boosted with startup bacteria.
It had a long nitrite cycle then was all fine.
I used to have very tiny patches of dino/cyano/hair (not that expert to differentiate) but nothing to be worried about.
My tank always had a high phosphate content (above test kit upper limit). All others parameters are fine, nitrates usually between 5 and 20 ppm. I heard it's due to some dead rocks that can leak phosphates.
Fishes doesn't seem to be affected, knowing that I have mandarin dragonet that are sensitive to grow.
My lighting is white with some blue lengths. White is for my mangrove pods. I run for 4 hours at 30-40% of it's max power and 1-2 hours to reach the plateau.
6 months ago, I took a bad decision by introducing a lot of macroalgae that I collected on the shore (lettuce, codium, and some mediterranean algae).
Since that moment, I had dino/cyano/hair growth to a point that it covered all my rock surface, partially sand, and inner tank walls are fully covered every 2-3 weeks.
My fishes are still fine, but my tank is very ugly and with a green tint due to that growth. My macroalgae got all eaten/competed.
I think of rebooting my tank because everty time that i try to introduce other special things like nems, urchins, shrimps, they all die with few days/hours.
I don't even dare to start corals as I know it will be a total failure.
I have a deep bed sand mostly with carbonate based sand but with a thin bottom layer of silica sand.
I never used chemical control products cause I believe such products may be one-shot while I wanna tackle the root cause of my tank unbalance.

What do you advice me to do ?
Thanks in advance.

 

[Lavey29]

Need complete tank parameters and some pics of the tank. White light promotes algae growth both good and bad.