Reef nutrition

New tank - Corals unhappy, water params look ok + diatoms?


Supporting Member
Hello BAR,
I just set up my first ever tank a little over 2.5 months ago, and have been having some problems since. I'll do my best to summarize in detail.

The tank was set up with Carib Sea live sand, and reef rock 2.1. I use the Red Sea blue bucket salt mixed with RODI water from my LFS. I've never used tap water in the tank, except for washing test vials and cuvettes.

About 2 months ago, I spotted a brown dusting (diatoms?) on the sand in a small patch, and its been getting worse ever since. It's been 2 months now, and there are no signs of the diatoms receding. About 1.5 months ago, I added three small frags of a GSP, Duncan and Zoanthids purchased from Aquatic Collection. The frags were dipped in Coral Rx for 10 minutes per the instructions on the bottle. 2 weeks ago, I added a pink goniopora from Neptune, and a green hairy mushroom given to me by @Galoot .

Thus far, I have had little success with the GSP, Zoas and Goni. All three corals look very unhappy.

GSP: opened up for a couple of days after adding to the tank, and closed up for about 3 weeks. Last week, they started opening up again, but some of the polyps have turned brown.
Zoas: some polyps open up partially, some have always been closed. A few days ago, I spotted some brown dusting on the polyps, so maybe they are being irritated by the algae.
Goni: The polyps extend only about 1/4 inch.
Duncan and Mushroom look just fine!
  1. Can someone please confirm of the brown algae in the picture below are indeed diatoms?
  2. What could be going wrong in my tank for the corals being unhappy?
  3. Is there something I can do to help get rid of the diatoms?
    I bought a bag of ChemiPure Elite, but i haven't added that to my tank because that would get rid of my phosphates and I don't want to risk dinos.
Tank: Fluval Evo 13.5
Lighting: AI Prine 16HD, running the Saxby profile at 30% max brightness

1x Ocellaris Clown
2x Trochus Snails
3x Nassarius Snails
3x Cerith Snails

Hikari frozen mysis cubes - 1/4 cube - daily
Reef Roids + 2ml Red Sea AB+ mixed together - daily

Temperature: 77 F
Salinity: 1.026 SG
Ammonia: 0 ppm
Nitrites: 0 ppm
Nitrates: 0-5 ppm
Alkalinity: 9 dKH
Phosphates: 0.03 ppm
Calcium: 460 ppm
Magnesium: 1305 ppm
pH: 8.6

ESV B-Ionic 2 Part to maintain 9dKH - Daily
Red Sea Magnesium to maintain 1350ppm - Weekly

Any help would be greatly appreciated.

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Coral reefer

Staff member
You have a new tank. Diatoms are normal.
I would make your own water so you know the di resin isn’t spent and getting lots of silicates.
Little to no nitrates and phosphates will make for unhappy corals. Especially softies.
This would be a good entry in a tank journal btw.
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Supporting Member
@Coral reefer , i get RODI from my LFS, and check for 0TDS at the store itself. If they have anything more than 0TDS, i dont get the water, and go to another store.
Do diatoms last 2+ months? Anything I can do to assist getting rid of them?

@ashburn2k I do weekly 10-20% water changes.


Supporting Member
The diatoms shouldn't last that long. The right side of your zoas don't look good. Are you running carbon? If not, try it and see if things improve.

Coral reefer

Staff member
0 tds doesn’t necessarily mean what you think it would.
I would say vacuum the sand when doing water changes and check for silca. You can do icp test


Supporting Member
pH is a little on the high side. I find 8.2 to be the sweet spot for my mix. Much higher and I get corals closing up.

Coral reefer

Staff member
I personally haven’t heard of 8.6 being bad for corals, but I’m not a zoa guy. I have a hard time thinking that’s your problem though.


Supporting Member
Yeah - i think the main problem is my insane diatoms / brown algae bloom and the <5ppm nitrates.
(I have an API kit for nitrates, and it has a 5ppm resolution. Waiting for Hanna to release the NO3 checker.)


Supporting Member
I wouldn’t trust those ph pen from amazon, get a real ph test or bring your water to someone live close by for a test.

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