Am I missing something?

So I have now been into this hobby for a year. Lord knows I have made manyba mistake in my journey so I have been constantly fiddling with my setup. But now I am curious as to if I'm missing something, which I most likely think I may be (filtration) wise.

I have a 120 gallon tank 4x2x2 w a 30g sump.
I use a gravitational overflow and. Mag drive 3 return pump about 350 gph.
In my sump I have a marine land 300 gallon an hour skimmer(only mech filtration I use)
I also have about 25 lbs of rock in my sump w 2 inch sand bed and 5 different types of macro algae and red mangroves.
Also use 2 t5 bulbs for lighting on sump.

I also have about 200 lbs of live rock in my dt tank.

I've been reorganizing which species fit in my tank and after my run to the store later I will then only have 2 tangs and 2 clowns and about 20 types of coral. I use 2 x 250 mh w pc lighting and led. I have 2 1050 power heads and 700 and a 240 in my tank so lots of water circulation.
I recently switched to spectra pure so now using 0 Tds water.

I've been bringing phosphates down from 2.0 to .5.
And nitrates I can't get below 20-25 ppm. So I am wondering if anyone can tell me something i may have overlooked.

 

You sound like you have everything covered fairly well. NA levels are usually linked to stocking and also feeding.

- Your stock sounds fine for that size tank, how big are the Tangs?
- How often do you feed?
- What's your clean up crew like?
- How long were you using tap water, what was your TDS like out of the tap?

 

A few things that pop out to me:

- Running GFO in a reactor can help bring those phosphates down to 0.
- Why are you only running a return pump of 350gph? Sump turnover rate should be about 10-20x of your DT per hour, meaning you need a return pump of around 1200-2000 gph.
- Whats the purpose of a 2 inch sandbed in your sump? If you're shooting for a DSB (which will aid in lowering nitrates) it should be atleast 4-5 inches deep.
- How often are you doing water changes, and how much % wise each time?

 

I also was questioning a Mag 3 return with that size tank/sump, I run a Mag 9.5 on my 70g with 20g sump dialed back a quarter.

+1 on what is your water change regimen

 

Water change since I got new ro unit has been 40% every two weeks. The guy at store sold me on the mag 3 said it would be enough it moves the water in and out ind a slow I thought. I wanted to stay away from running more media like gfo and carbon if i could to keep it simple but hmm... Usually wc is 20% every week

Tangs are about 5 inches. Feed once a day 1 mysis or brine pellets and seaweed. Cleanup crew is about 25 snails. 15 hermits 2 skunk 2 blood and 3 peppermint shrimp. Also got a serpent star another type of star.

 

Im thinking your may have made yourself a nitrate factory in your fuge. 25lbs of LR in your sump is a lot, combine that with your low return rate and your have a good place for crud to accumulate. I'd remove that rock over a months time and perhaps replace it with a nitrate absorbing algae (chaeto or mangrove).
Your return rate may be a little low I would not stress that part too much but I would think about up'ing it buy 2-300 gph just to get some good gas exchange, but i run my tank at a low return rate as well to get better performance out of my skimmer.

And when you get your nitrates down you can probably cut back on those large scale w/c. 20% per month is often the norm but every tank is different.
GL!

 

I agree, up your sump flow rate, but I'd aim for a minimum of 10x, so about 1200 gph. I'll bet your skimmer doesnt perform very efficiently either...

 

Sorry your quite wrong on the skimmer part. It gets about a full cup once a week. Now I have over 10x turnover in the dt tank. The sump is gravitational fed and if I had a pump 1200 gph the feed wouldn't be able to keep up. I've also read / been told this the slower return will help my skimmer by allowing it to remove more crud due to slower waters. I'll take your advice on sand in sump and removing live rock. Can I just add new sand on top of old sand? Will it start a cycle or do it very slow like the rock.

 

its 10X sump volume per hour @ head witch mag 3 is low i would invest in a 9.5 may have to dial back a bit what im wondering even though flow rate is low possibly the flow arround the macro algae is high wile flow arround the skimmer is slow

how is your sump setup (possibly change flow areas in the sump)

and feeding habbits

 

A Mag 3 would work fine if the return plumbing was 1-1/4" or larger. What size is it currently?