Substrate question

[briterco]

Hello,
My 125g has been up for almost 2 years and has been doing well. However, I'm having a slowly upward creeping of nitrates, and I believe it is a problem within the sandbed. I have about 100# live rock, a w/d filter with a small fuge inline, and a skimmer. I've stripped and cleaned the w/d a couple months back, the skimmer says it is for 125g tanks, but I suspect that it might be a bit small. I had routinely been going 5% water changes weekly. About 3 months ago I started doing 10% weekly with deep vacuuming of the sand.
The sand is about 1 1/2" deep. It came as part of the aquarium "kit" I purchased from the LFS (if only I knew then what I know now!). It was about 50# live sand and 50# crushed coral. The live rock sits on top of the bed. I think the mix of CC is part of the problem, along with the LR sitting on about 75% of the sand surface. Also, from what I understand the bed is not deep enough to truly process out the nitrates. At this point, I'm considering removing the bed entirely and either going bare bottom or replace with minimal coverage (1/2"). Is this a good idea, or am I heading for trouble? The other option is, should I just add ore live sand to build up the bed in there now to make it a real deep sand bed (4" deep)?
Would really appreciate any thoughts. I would like to start working on this over the weekend.
Thanks!

 

[jmick]

The problem with CC mixed with sand is that eventually the sand will settle to the bottom and your right that the 1.5” really isn’t deep enough to be beneficial. I really don’t like the way bare bottoms look and I don’t like the idea of dumping more sand on top of the existing substrate (if tank were only a few months this would be a good option but I’d be worried about trapping a lot of detritus under the new layer which may cause issues down the road). If it were my tank I’d probably pull the majority of the substrate out and put in new sand (Oolitic) to a depth of 4-6” and I’d skip putting in live sand because your rock and the remaining sand will seed it quickly.
Last year I pulled my substrate out and put in a DSB and it was a lot of work but it’s been really beneficial and I’m very pleased.

 

[jmick]

Also, if you are going to take out or add new substrate I HIGHLY recommend setting up a temporary tank for your livestock during the transition.

 

[briterco]

Thanks for the comments. A couple of questions...
Does a LFS typically stock Oolitic sand, and if not, where can I find it?
Would you recommend pulling all of the current substrate out at once, or smaller sections over a period of time?
Once I've removed some substrate, do you recommend resetting the live rock on the bare bottem and adding sand around it, or put in the sand bed first, then set the LR on top?
Thanks!

 

[jmick]

The LFS I go to carries it in 50lbs pails that go for $40 and I’m sure one in your area will supply it. I’d pull it all out at once and be done with it. It took me a full Saturday to do it. I pulled all of my live rock, then put all my critters in a holding tank then I took out most of the water then the substrate. I drained a lot of the water into a holding tank so I could reuse it rather then fill up all 50gal with new water. Once all the CC was gone I emptied the rest of the water, which was rather foul. Once this was done, I refilled with the water I had originally pulled from tank then I put in the bigger pieces of rock and dumped in my sand. It took almost 4 days for the water to clear up and at this time I put all my rock work back in and I began to run my filter and skimmer. Adding the rest of the rock did stir up the sand again and I waited 6 hours before I put my critters back in.
It’s a really big job but if you have everything ready before hand it should go well. Just make sure you have a holding tank set up because you will need it for a few days and premix extra water before hand.

 

[briterco]

Can you tell me more about setting up a holding tank? Can I go as simple as using some rubbermaid containers? I have a 10g hospital tank now, but certainly would not want to cram everyone in there, even for a very short time. Do I need to aerate and or filter the water while they are in holding? Certainly I'll reuse tank water so as to not shock them in moving around.

 

[carshark]

also you stated that you deep vaccumed the sand bed, that could have killed a lot of your nitrifying bacteria...

 

[carshark]

you can use a rubbermaid, which is almost preferable because it is less stressful for your organisms with all sides opaque. put a powerhead, heater, and maybe a small hang on filter but it isnt neccessary because they will only be in there for a short period of time...