High phosphates in 4month old tank

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Sayanta

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Hi, I am running my 20g tank for 4 months. I was seeing a lot of cyano(?) before, I had turn of the light for 3 days, scrap it as much as possible, siphon them out. Now I would say they are under control. But glasses are getting thick layer of brown algae every day. Don’t know what kind of algae they are, is it part of the process. I tested my water with LFS, got high phosphate. High magnesium ( it is actually always high, got little bit down 1450 once).
What should I do? Should I just do regular water changes to reduce it? Or use chemipure kind of stuff? I am new, seeking for suggestions.
Another thing I want to mention, recently I have removed a bunch of Gracilaria macro algae, because my Emerald crab just eating it constantly, and molting and growing too fast. It also creates a mess so I remove it. Could that also play a spike in phosphate?
Attached test results here.
 
20250610_145054.png
 
What is "high" phosphate? Can you please post your parameters? Pictures will help too to identify the algae.
 
What is "high" phosphate? Can you please post your parameters? Pictures will help too to identify the algae.
I don’t have pictures of the algae right now
 
A 4 month old tank is basically at the peak of the "uglies", and there are likely a few different algae's growing in the tank. Control it with good water movement (do you have powerheads in the tank?), good clean up crew (get more snails as more algae grows), frequent water changes, feed very small amounts to the fish, only as much as they can eat in about 30-60 seconds (but feed multiple times).

The phosphate is slightly high which can be controlled by phosphate remover.
 
A 4 month old tank is basically at the peak of the "uglies", and there are likely a few different algae's growing in the tank. Control it with good water movement (do you have powerheads in the tank?), good clean up crew (get more snails as more algae grows), frequent water changes, feed very small amounts to the fish, only as much as they can eat in about 30-60 seconds (but feed multiple times).

The phosphate is slightly high which can be controlled by phosphate remover.
I would say water movement is good. I might have over feed my fishes. I am concerned about if I use chemipure kind, could it abruptly reduce phosphate? Should I remove it after few days with checking it time to time? If I remove, can the phosphate revered back again? May be I am thinking too much
 
I'm not sure that phosphate level warrants action, but lowering it is a fine plan. Water changes will not be very effective. Unless you dose N somehow, you'll need to use a binder of some sort, such as GFO. Growing macroalgae cannot lower it a lot without bottoming out the nitrate that is presently at a fine 14 ppm.

This has more:

https://www.reef2reef.com/ams/randy’s-thoughts-on-nutrient-target-ranges.1087/
 
Rocks can absorb phosphate and then slowly leach it out afterwards. If you used dry rock to start your tank, then this is possible the source of the phosphates. Its easy to test this by putting a couple of the rocks into a bucket of new saltwater and then test, if the rocks are leaching then phosphate will slowly rise in the new water.

I've never used chemiclean so I don't know about it, but it is popular and others here have used and can offer suggestion. I use either gfo (something like rowa phos) or lanthenum (something like phosphate-e). Drop the phosphate level slowly over time.
 
Could be the tank maturing. I could clean my glass daily on all of my tanks if I really wanted to. I've never considered algae growing on the glass a bad thing.
This is one tank that shows how bad the glass gets after 2 days. I've been letting it go for a week now since my bristletooth tang has been eating it. The algae is green under whites.
PXL_20250117_232855438 (1)~3.jpg



Your numbers are very similar to one of my tanks that's been running for a bit over a year and I have zero nuisance algae so I just keep an eye on things. Sunday tests were NO3 25.6 PO4 0.53
JMO but I think often what some consider elevated N and P get blamed for causing nuisance algae when it may be other things, often lack of herbivores.
 
Could be the tank maturing. I could clean my glass daily on all of my tanks if I really wanted to. I've never considered algae growing on the glass a bad thing.
This is one tank that shows how bad the glass gets after 2 days. I've been letting it go for a week now since my bristletooth tang has been eating it. The algae is green under whites.
PXL_20250117_232855438 (1)~3.jpg



Your numbers are very similar to one of my tanks that's been running for a bit over a year and I have zero nuisance algae so I just keep an eye on things. Sunday tests were NO3 25.6 PO4 0.53
JMO but I think often what some consider elevated N and P get blamed for causing nuisance algae when it may be other things, often lack of herbivores.
You have a beautiful tank. I am also learning. Will keep an eye on the parameters
 

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