Dinos and/or diatoms?

[UnnamedReef]

My tank is ~8 months old and I had a bout with Prorocentrum dinos 2 months ago. At one point they had taken over the rocks but were always concentrated in the sand bed. Two 72 hour blackouts + UV knocked them back, and silicate dosing and keeping PO4 around .08 (Hannah) and nitrate around 10 (API) kept them back for that two months period.

I went away for a few days and my nitrates bottomed out. I'm seeing some red-brown spots in the sand bed again, sure looks like the Prorocentrum from before. I took a few samples and I'm seeing three things:

- short, skinny, pointy tube-like organisms. (Diatoms for sure, not shown in photos)
- a few large dinos (or, what I believe are larger dinos). They're on the left side of the microscope photos.
- some small, circular diatoms or dinos. They seem to out populate the larger dinos by a wide margin. I'm hoping these smaller organisms are diatoms and a result of the silicate dosing. Can anyone confirm or advise? Photos and videos attached.

Thanks!

 

[Lavey29]

https://www.reef2reef.com/attachments/dinoflagellateid12_12_2019-pdf.1324729/

 

[UnnamedReef]

Thank you. The main 3 types are all similar in size, I'm thinking the large two organisms in the slides are Prorocentrum, what do you think?

Being much smaller, that would make the small ones either diatoms or SCA?

 

[Lavey29]

Thank you. The main 3 types are all similar in size, I'm thinking the large two organisms in the slides are Prorocentrum, what do you think?

Being much smaller, that would make the small ones either diatoms or SCA?

I have old eyes so it's hard for me to tell but I think your conclusions in your first post are probably accurate. I would stay the course maintaining proper nutrients levels. Dose pods once or twice a month. I use PNS probio which is a natural heterotrophic bacteria that eliminates organic waste so junk in the tank is not helping the bad guys. I dose this once a week. I'm not a fan of UV but it can help with dinos that go into the water column but not dinos that disappear in the sand overnight. But it kills good guys to along with bad guys. 8 month tank is still unstable. Stick with weekly water changes. When my tank hit one year it became much more stable and predictable.

 

[UnnamedReef]

Great, thank you! I haven't been doing water changes fearing that I'd replenish trace elements and give the dinos a foothold to get back. I'll start doing them every other week and see how it turns out

 

[Lavey29]

Great, thank you! I haven't been doing water changes fearing that I'd replenish trace elements and give the dinos a foothold to get back. I'll start doing them every other week and see how it turns out

Just like 15% with sand siphon. Maintain nitrates 10 to 20 and phosphate at least .1. Ideally the ratio you want is 100:1 nitrates to phosphate. So 10 nitrates to .1 phosphate. I dose phytoplankton daily in small amount to sustain my tanks pod population. In between water changes turkey bast the top layers of sand a little.

 

[taricha]

Can anyone confirm or advise? Photos and videos attached.

third video showing dinos does look like a couple of prorocentrum cells.

most of what's in the video are neither diatoms nor dinos but another zooming photosynthetic single cell called cryptomonas/rhodomonas

These are not a dino. They are another random harmless flagellate. Something like a cryptomonas / rhodomonas.
Here they are in a couple of vids from my system, shape and movement a lot like yours:

(Close-up):

 

[UnnamedReef]

This is why I ask the experts, thanks! I'll go with some manual removal through a 5 micron sock to clean up the sand. I've kept up MB7 and SpongeExcel dosing to keep the dinos back, seems like that's working if I can only find two on the slide.