high no3 and low po4 :(

350 mA for starting the screen. After that, you can jump to 700mA as long as you don't "burn" the screen.

My recommendation has always been for 700mA drive current, but when you start a brand new screen (one with zero growth) then you generally need to run at a lower drive current, or add a diffuser until you get consistent growth (meaning, the "holes" in the screen are filled in with algae, and they stay filled after the screen is scraped)

Do you clean your screen every 7 days? Or do you wait longer sometimes?

Do you have any pictures of the screen right after you have cleaned it?

Do you just scrape the growth off, or do you scrub it with a brush?

 

I can see part of the issue. With my screens, after about 6 weeks, almost all of the holes are filled in and stay filled in after scraping. The algae growth grows from these pockets of algae.

Your screen material here has holes that are too large, so when you scrape the algae easily gets pulled out. The larger holes mean less surface area also. You can see in your pics above that the parts of the screen that are lower down have very few holes filled in.

I use a 2 step roughing process and have been told by many that when they get my screens, they had no idea what "really rough" was.

I am not sure how the flow looks while it is running, which is why I wanted to see a video of this. I have a theory, but I want to see if the video confirms it.

When you do make the video, remove the LED fixture from one side and turn the LED fixtures off. Use a regular white light (flashlight, desk lamp, etc) when recording so that I can see the flow and growth.

Also - how old is the Live Rock in your tank? How much do you have in there? Have you added any new rock or sand to the system in the last year?

 

Ok, that is another piece of the puzzle here.

So what happened to the rock in your old tank, that was running the original scrubber?

What might be happening here is that your new DIY rock, new to the tank in October, could be absorbing nutrients out of the water. This is a known phenomenon. So this might be the reason for low phosphates - possibly.

This still does not explain the high nitrates. However I believe this is still related to the scrubber. It could be the screen material, the LED lights, or the flow, or a combination of all of these. These are all very important factors

Regarding the screen - you want the #7 Darice Plastic Canvas, and nothing else.

As far as roughing it up goes, you should do this in 2 steps. The "old" way (which was using a hole saw) is inadequate, in my opinion. Step #1 should be using a wire brush to take the "shine" off the screen, deep into the holes. I use a wire brush attachment on a drill while the material is clamped down to a work table. I run the drill at a low speed, and only make a few passes.

Step #2 is using a sharp-tooth saw blade in small overlapping circular strokes. I made a video of this process but haven't had time to post it.

Like I said though, I can do this for you and send you a roughed up screen if you have a hard time finding the material.

Take the video now - it doesn't matter where in the "growth cycle" you are.

I would let the scrubber grow more before cleaning. Perhaps 9 or 10 days. As long as you are not having algae detach, let it grow, for as long as 14 days. But, first, let it grow for 9 days and clean it and make sure that you are not getting any dying algae close to the screen, or weak attachment.

 

Ah, ok - 3 year old rock it quite different! I misunderstood

 

My original thought was that the rocks were absorbing the phosphate by way of precipitation of calcium phosphate. This might still be happening if you are adding phosphate to the system.

I am concerned about you adding the phosphate. This should not be necessary. If you are adding food, you are adding phosphate. Phosphate is in all food, it is converted from organic to inorganic by the inhabitants. There is also a process which converts inorganic to organic, I believe @Ace25 touched on this in the past.

Many reefs have very low to undetectable (by hobbyist grade kits) levels of phosphates, so having these at a level that is not detectable in your aquarium does not mean it is not there.

I fear you may be creating a future problem by adding phosphates to your tank. I would consider needing to do that a 'last resort'.

 

But @Ace25 in theory, if a scrubber is growing algae fast enough and at a high enough volume, shouldn't it be able to be the sole source of nitrate removal?

 

Yeah I wasn't necessarily thinking of scrubber and absolutely nothing else, but in general on a reef system where you have an appropriate amount of live rock, and an appropriately sized scrubber, that can be all you need. If your tank is short on rock per unit of water volume, you should be able to compensate for that with a larger scrubber. If you take it to the extreme, and have a massive amount of live rock (or other bio active surface) then you can, in theory, do without the scrubber. But the reverse is not necessarily true, or like you said, the scrubber would be ridiculously large.