Help with algae ID!

[AxeMedix15]

Let me start off with, I know to have a 100% positive ID, I need a microscope however I do not have one and have no access to one so I understand this will all be best guess only. BUT…

Can I have everyones best guess on what algae Im dealing with here? Tank is 75 gallon and started about 6 months ago. I went through the ugly phase without issues. Lately this algae has been showing up on my sand bed and glass noticeably getting worse with my lights on. If I leave it alone bubbles will start to emerge on the glass. When the lights are off it seems to go away. With this, I figured I was dealing with the dreaded Dinos.

I turned off all my white lights and have been only running blues, feeding heavier, and paused my skimmer. This is where I need everyones opinion. Obviously I still think im dealing with some Dinos BUT am I crazy or does the sand bed look like diatoms? If it is diatoms, I feel like my treatment is working and the diatoms will eventually starve out the Dinos. Is this correct? What does everyone think? Thanks for any input!

 

[EnterName]

Dinoflagellates

A nightmare in established tanks, but very common in young ones. Don't stress about it too much. Keep nutrient levels stable (at desired levels) and they will most likely disappear on their own.

If the problem persists for a few months, you can think about UV sterilization, silicate dosing, Redox/ORP boosting, and all those things people usually recommend. For now, I would limit myself to keeping parameters stable, as messing with new tanks often does more harm than good.

Yes, the sand might have some diatoms as well. Silicate may be increased. It isn't clear from your post if that's intentional. Just in case you want to get rid of them, you will need to bring silicate levels down again.
Adsorbers unfortunately also drain phosphate, so make sure you aren't running into a phosphate limitation if you try adsorbers. I don't think it's necessary to act besides ensuring your RO/DI is absolutely free of silicates by measuring TDS or conductivity. Oh, and I would keep the skimmer running for gas exchange.

Diatoms are sometimes used to get rid of dinoflagellates but the effectiveness of this method depends on dino species and number of diatoms. Small numbers don't really have an effect or might be beneficial to some dinoflagellates as they can prey on diatoms. I don't know if you have reached the threshold at which diatoms will outcompete dinos, you will have to keep observing.