Algal blooms after switching from LFS water to DO/DI system

[RainbowManatee]

Back in March I bought a 75 gpd 4-stage RO/DI system after using LFS water for the ~1.5 years since I set up my 25 gallon aquarium. After a few water changes (5 gallons per week), I started having diatoms return within hours of the water change and they progress and get bad over the course of about a week. I've always had some diatoms show up between weekly water changes, but this is getting insane. Below are some pictures about a week after the last water change and it seems like the problem may be getting slightly worse. My guess is this is a problem with silicates not being completely removed from the tap water and via my RO/DI system. TDS of water is 0.

If silicates are the issue, would adding another DI resin be enough to help with this or would adding an anion resin be a better option? I've been wanting to add another DI resin anyway to decrease the amount of waste water I'm producing. I tried adding GFO to the aquarium and the water change water to try to strip the silicates, but doesn't seem to have helped. The worst part may be that I got a slacker conch!

Over the past several weeks NO3 and PO4 have remained pretty stable at ~6 and 0.5, respectively.

Thanks!

 

[goosemans]

I think that’s dinos, I could be wrong

 

[RainbowManatee]

You might be right. I've been wondering if they might be dinos. I guess I better do a black out...

 

[PharmrJohn]

Can't really make it out, but are there snot like bubbles present? Also, does the issue look to go away when the lights are out, then come back when lights come on?

Edit: What's your flow look like in your tank?

 

[RainbowManatee]

There hasn't really been snot like bubbles. The algae on the sand bed is always there, but stringy strands of algae appear during the day and don't seem to be present when lights are off.

Flow is the stock aquatop return pump (650 gph I think?) and a hygger wavemaker set to lowest wave settings since its a small tank. Maybe I should increase the flow at night on the hygger once the corals are retracted?

 

[thedon986]

Do you track and trend your nitrate and phosphate? I make sure to always check them before a water change so I don't bottom out.

 

[RainbowManatee]

Do you track and trend your nitrate and phosphate? I make sure to always check them before a water change so I don't bottom out.

Yeah, nitrates and phosphates have been consistently around 6 and 0.5 ppt, respectively over the past several weeks after a water changed. They've never bottomed out. I checked this morning and NO3 was 9.5 and PO4 was 0.03, but water hasn't been changed in a week. Changing the the water now and hoping to remove as much algae as possible then starting with a 3-day blackout with peroxide dosing as a first step. Thanks!

 

[thedon986]

.03 phosphates could be low enough or actually zero with testing variance to bring on dinos. Those don't look like diatoms since there is strings. Maybe cyano but I would say 95% chance they are dinos.