Use of PVC / plastic elements - leaching issues?

I doubt your plastics have silicates in them... unless you're using fiberglass... it is usually sand and glass that leach silicate. Plastics will leach phosphates which causes an algae bloom (usually film algae or any other algae that is present in your tank may take off).

Some people think that plastics like eggcrate will leach MORE phosphate as the get older and start to break down and decompose when exposed to light. I don't know if anyone has tested this, so it may just be anecdotal, but it makes sense if you think about the nature of plastics in sunlight.

PVC is supposed to be basically inert, though.

Diatom blooms just happen in newly set up tanks. If you have a skimmer, they are very effective at removing diatoms... personally, I'd rather have a diatom bloom that can be removed with a skimmer than most other forms of algal growth.

 

RE: adding new rock... I don't think you'll experience any die-off by adding dry rock, so you won't get a cycle in the traditional sense. I just added about 50lbs of dry rock to my tank, and the tank has actually cleared up and nitrates have gone down... I believe this is due to the greater surface area for bacteria to grow.

Rinse the rock so there are no particles on it that wind up in your tank. When you put the rock in, you will get bacteria blooms that will take away unwanted nutrients, but shouldn't put them back in... so any 'cycling' that occurs can only be good.

 

I really appreciate the replies so far! Thank you As usual, I am learning a lot.