View Full Version : Greenish-yellow hard spots

07/04/2017, 10:15 AM
Hi everyone! I have an established 36-gallon acrylic saltwater tank. I'm having a serious issue with these hard greenish-yellow spots that appear on all sides of the tank. I'm usually able to scrape them every other day, but I went on vacation for a week and came back to an outbreak. It's all over the tank. What is this, and can I prevent it from happening? Doesn't seem to bother the fish, but it's ugly as heck. Thanks!

07/04/2017, 02:08 PM
That sounds like coralline algae, although there are a number of other possibilities? Does it come off the wall in a sheet if you use a credit card? Be careful not to scratch the tank. Coralline algae should be rock-like and will fizz in vinegar. It's also very flat.

07/04/2017, 04:08 PM
Thanks for the reply, Jonathan! No, it doesn't come off in a sheet. I have to actually scrape them off, and it's extremely tedious.

07/04/2017, 04:20 PM
Here's a pic!

07/04/2017, 05:41 PM
Those look like thin spots of early coralline growth. With some luck, the growth might slow down or stop on its own, or you could try a bit of GFO as an easy first step.

07/04/2017, 06:50 PM
Thanks! I've never used GFO. Can I get it locally?

07/05/2017, 03:50 PM
Most fish stores will carry some version or the other. PhosBan and RowaPhos are two of the more popular brands. You will need a power filter or the like to hold the media and force water through it. If the cost seems a bit much, you could wait for a bit, as well. GFO is not a sure cure, in any case. Is there much food going into the system?

07/05/2017, 05:43 PM
I have 4 fish, and I give them one small pinch of food pellets a day.

07/05/2017, 07:17 PM
Okay, some GFO might help.