HELP - Brown spots on live rock

[Astacey7]

Hello,

I’m newer to saltwater tanks and have absolutely loved everything about it. I’m having trouble, and could really use suggestions. I have a Waterbox Cube 10 that is going on 3 months. The tank currently houses a clown, purple fire fish, shrimp, mini conch, and 2 turbo snails. Levels never seemed to fluctuate until recently, nitrate being the only fluctuation and levels are between 10-20ppm. Any suggestions on curbing the brown spots? One of my coral is on day 2 of not fully opening. Is it due to the nitrate levels? Adding to much coral over to short a time? I have a Duncan that was added over 2 weeks ago, however there are 4 new heads starting to grow. I’ve reduced feeding as it is possible I have been over feeding. Any help is greatly appreciated!

 

[attiland]

Without a microscope it is hard to say what it is could be Dinos.
If you think it is affecting corals best to add activated carbon to the system.

used microscope is about £30 on eBay and helps you be sure what it is

 

[vetteguy53081]

Looks like typical diatoms especially if tank is new(er) and typically appear in a reef tank that has just completed its cycle but they can also appear in an established reef tank. They can cover sand, rock, pumps, glass, you name it. Diatoms look ugly but in most cases they are harmless so the key is to not panic when they appear.
Diatoms feed mainly off of silicates but also consume dissolved organic compounds, phosphate and nitrates. Unfiltered tap water can contain silicates and is a good way to jump start a bloom if you use it to mix salt or to replace water that evaporated from the tank. The best way to prevent this from happening is to filter water through a RODI unit, although you can still get a diatom bloom when using RODI if the cartridge that removes silicates expires.
diatoms are typically harmless to a captive reef and can be beaten once their food source expires. Once you put the kibosh on the source, the outbreak should last a couple of weeks so just be patient and it will pass. For major outbreaks you may want to consider the three day blackout. Diatoms are easily wiped from the glass with a mag float, a turkey baster or a toothbrush can access other areas of the tank. Be prepared for them to re-establish themselves quickly, they are likely to be able to resettle and have exponential growth rates.
To prevent their return, practice good aquarium husbandry by doing regular water changes, keep the substrate clean, don’t overfeed the fish, ensure your skimmer is running at an optimal level and rinse out filter socks and sponges on a regular basis.
Some cleaner crew to help control it are : Cerith snails, Nerite snails and Trochus snails and also Astraea snails are effective at removing diatoms.

 

[Astacey7]

Thank you! All of my water, both salt and RODI, come from the same LFS that all material has been purchased from. With the current level being minor, is it worth subduing with a 3 day blackout? Or is it better to limit feeding and increase water changes? Do I need to dose carbon? Thank you both for your input!

 

[attiland]

If diatoms it will go by itself if Dino you need different action. Carbon will do no harm