Soft corals wont grow

I have had a pair of red mushrooms for 4-5 months and they won't grow in size or in numbers. The same can be said for my blue mushroom. It put off a new mushroom about a month ago, but it hasn't gotten any bigger than when I noticed it a month ago. I have a mat of star polyps that hasn't grown since I got it 3 months ago and my GSP, while I've only had it 2 weeks, hasn't grown a bit.

My monti, candy cane, favia, coraline etc. are growing very slowly, but noticeably, unlike the softies.

The following numbers have been, more or less, consist for the last 2 months:

Nitrate: 0
Nitrite: 0
Phosphate: untested (I've never had a lick of algae in this setup)
Salinity: 1.026
Temp: 79
Calc: 410
Alk: 10.1/3.6
Mag. 1372
pH: 8.3
Tank: 20 gallons
Flow: 400 gph Koralia
Light: 55 Bridgelux RGB LEDs @65-75% output
Light cycle: 10 hours
1 Sabae Clown
1 peppermint shrimp

It's been a couple of months since I've done a water change, btw. Could I be depleted of trace nutrients that is causing such a low growth rate? Lack of flow? Too much flow? The tank water is 18 months old, but I've only had corals and fish for the last 6 months.

I'm probably being impatient and expecting too much. But I can't help but think of what I can do to improve my growth after seeing others fast success, both on here and at my local Local fish stores.

 

Its probably not enough nutrients. softies dont do as well normally in a clean tank.

 

Well I'm not about to dirty my water lol. I ripped apart my original set-up 3 years ago from uncontrollable algae conditions. I just introduced the fish and shrimp within the last week or two. Maybe the feedings (didn't feed the tank before that) will help provide some nutrients for them?

 

I think I'll do a water change today. Just in case Im missing trace elements. My iodine is at .09, possible issue?

 

Possible photoinhabition.

Feature Article: Water flow is more important for corals than light. Part II: The science of corals and water flow — Advanced Aquarist | Aquarist Magazine and Blog

 

Do you dose anything for trace elements? If you don't and you don't do water changes, you are probably right that the lack of trace elements could be your problem.

 

Salifert makes a product called Trace Soft I use that along With Trace Hard since I have a mixed tank and my softies are growing like mad Zoa's double in size in a months time and had to trim my GSP last night since they where getting to close to some other corals. Don't know if it's Saliferts products helping or not but both LPS and SPS are growing. I only due a water change every 3-4 weeks.

 

Great article! I have a Kent trace that I try to avoid using since I can't test for them.

How much total flow should a 20 gallon have?

 

Should I double my flow? From 400 to 800 gph?

 

that's why I opt for more frequent water changes.