trouble with growth

So for clarification, your "8 on 4 off" was repeated twice per day for a sum total of 16 hour on and 8 hours off for each 24 hours period, correct?

If so, then I would combine the 2 photoperiods, so 16 on (one block of time) and 8 off, reverse of tank photo cycle.

 

Correct

 

I don't want to jump to a conclusion here - need more info.

The "black" growth that has been talked about in relation to a high-nutrient tank is a thin, almost oily looking growth that coats the screen and flakes off when you scrub it, and is sometimes hard to remove - and the screen material is bare white under it. It has almost no volume, it's like a sheet growing on the screen material. Is that what you are getting?

Or are you getting at least some mass of growth, but it has almost a slime layer over it that is rather dark and gooey, and smelly (like dinos or cyano)?

 

I've seen this stuff before. It almost looks shiny or glossy, and stays that way when you remove the screen from the water flow. If you "swipe" your palm across it, or if you swipe a scraper or credit card across it, it comes off. Beneath it is usually hair algae.

Is this what you are seeing?

 

I'm just making sure that you understand the difference between the black-oil algae that has been historically tied with high-nutrient tanks. That stuff looks like this


and when you clean it off, it looks like this:


So you don't have the black oil growth. You have dinoflagellates and/or diatoms growing over the top of the algae mat. Light does get through this kind of growth so it is not something you need to scrub 100% clean every 3 days like the black stuff (which I should note that I have never seen personally).

What I would do in this case is leave the photoperiod as is. Check the screen at about the 4 day point. Remove the screen and give it a swipe to rid the dinos and a swish in water to release loose growth, but don't scrape. Try to promote hair algae growth and deter the slime growth by rinsing it away. You might let the screen grow a bit longer before doing a full cleaning while doing this procedure.

I'm wondering if there is some parameter that is off in your tank. Have you ran a full battery of tests lately?

 

It has nothing to do with your RODI. It may not be dinos or diatoms but it is something along those lines that grows well in the scrubber conditions. I do believe it is dinos because if you have ever had them in your tank and sucked them out with an airline hose, then you know exactly what they smell like, and the smell is the same. I get this type of growth over the algae mat on a regular basis. Sometimes worse than others, but it is dark brown to black goo and it easily disintegrates when disturbed.

 

It has a pretty distinct smell, pretty strong, but dissipates rather quickly.

I think 14 hours should be OK.

The only other thing to note is that when I first starting my UAS test unit, and I was playing with the photoperiod, I found that I would get a lot of this 'dino' type of growth when I was running a photoperiod that was too long. At that time, I was getting very little green growth, and remember this is a UAS and the screen was pretty much bare (and we didn't know what kind of result to expect).

I don't see that anymore, hardly at all, on my UAS which now will grow a consistent green mat of algae.

On waterfall units, I will also see this dino-type growth and it is usually over the top of the green growth, a thin layer, and the growth under it is not inhibited.

Diatoms do grow long and stringy also, and they are probably one of the most basic forms of life on earth, and grow quickly in the right conditions. So it could be either one (it actually probably is diatom).

Anyways, my theory is that if you give it the right conditions, it will grow, and the scrubber provides those - for diatoms, dinos, GHA, turf, etc. From what I have seen on many different units I have ran, growth and nutrients available are strongly tied, as well as some water parameters like alk and potassium. When you run the lights too long given a certain condition set, you can get an over-abundance of one type of growth.

So it's hard to diagnose what could be going on without knowing your water parameters. Since you've been having trouble getting green for so long, I think we need to back up the bus and know where we are starting from.

Test N & P, Alk, Cal & Mag, and K (potassium) if you can.

I recommend Salifert for N, Cal, Mag, and K (only Salifert for K)
For Alk, Salifert is very good, Hanna Checker is best
For P, Hanna Checker Phosphate or Phosphorus is the only one I would use
Can use API for N, it will tell you if you have a problem or if it's really low, Salifert for very low range resolution though.

 

I keep track of Alk in dKH. From RHF off RC

...or multiplying by 0.056 (which is what I do to convert my Hanna meter reading)

So you were at about 10.3 dKH, not bad, within spec

Calcium and Mag, wow those are low. Are you sure on that mag reading? I'm not sure that mag that low is even possible, especially if it was recently spot on from AWT. Remember the Cal and Mag kits are sort of reverse logic, the more drops you add, the higher the level is, the chart is based on what is left in the titration syringe not what was used. That would have had the color change happen within the first few drops of titration - crazy low. Just checking, I've consulted with a few people who read it the other way.

 

Oh wait I just recalled that you said you had precipitation in the tank - that might explain low cal and mag. What doser was stuck on??