quickly rising phosphates - what to do?

[Dave MN Nano]

I have a 20 gallon nano with fish and soft coral and LPS - 9 months old. I have a fair amount of rock and sand so I probably have around 15 gallons of water.

 

My nitrates have historically been 0 or very difficult to measure on Seifert test kit, and phosphates maybe 0.03 on the Red Sea test kit. I heard that I should have higher nitrates - target 5 PPM for my corals.

 

Here's what I did - doubled feeding, turned refugium light way down, eventually to 1 hr. per day, and did no water changes for 5 weeks. No change for the longest time.

 

Then suddenly::

 

6/6/21 Nitrates 5 and phosphates 0.05

3 gallon water change

Cut feeding way back

Refugium light back on 9 hrs a day.

6/8/21Nitrates 5 and phosphate .10

5 gallon water change

6/11/21  Nitrates 7.5 and phosphate 0.10

7 gallon water change

Nitrates 5 ppm and phosphate 0.12

 

Have I created a phosphate monster? Any suggestions??? I am now seeing first several wisps of hair algae and first 4 or 5 bubbles of what I think is bubble algae.

[Jaren45]

any reason you turned the refugium down? like you mentioned I would imagine that would just let nuisance algae pop back in.

 

i'd go back to running it normally, and if its too effective just up your feeding or add another fish if possible.

 

also i'd stick to a specific water change amount and do the same every week or biweekly if possible. routine is really important for the health of our tanks and skipping water changes can add up quickly even if your coral look fine visually.

[jservedio]

You just wildly overcorrected for a very slight problem. You essentially doubled your import of N and P and entirely eliminated your export. Go back to exactly what you were doing before hand and wait for your N and P  to come back down - it's probably going to take a few weeks, especially if what you were feeding wasn't being immediately eaten and is now decomposing in your sand and rock. When it stabilizes, then you can consider either slightly increasing feeding, very slightly reducing the light on your fuge, or slightly changing your WC schedule. Only pick one! The key is to make very small changes and giving them time to work.

 

Also, if you started your tank with dry rock, you are right in the range of time where the rock and sand will stop absorbing phosphate.