concrete blocks?


New member
i asked this same question at the local reef club forum and no one could really give me a straight forward answer....

could i use concrete blocks as base rock?
some people told me, maybe, if i cure it in water for a couple months??
reason im asking, the city aquarium is using them as base in their big reef setup and it looks awesome...
it would also save me tons of money on base rock.

I remember a few years ago some guy put a huge concrete blocks in his tank and he had all kinds of problems and not to mention all the people that were flamming him. I would just buy some lacerock and use that as your baserock. It only cost $1 or $2 a lb and isn't that expensive at all. What size of tank do you need the baserock for?
IMO donot use it, there are alot of "bad" things in the mortor/cement they use. Talk to the people that run your city aquarium, and get some answers from them, I do and it is a great source of info since one is a Marine Biologist.
Yes, you can use concrete blocks. They will likely raise the pH in the tank and so would need to be "cured" by a nice long soak in H2O--a month or more is likely.

As stated above, however, you really don't know what impurities may be in the blocks. I would recommend just making you own concrete baserock. They will still need soak time, and there is some effort involved, but I have seen some amazing tanks done with concrete mixes. There is some great info in this thread:

It has split a few times, but it is worth the read. A little practice, and you can very cheaply make a great base formation.

Edit: On the last page of the link above (page 6 for me) Insane Reefer has posted a nice summary methods and tips.
Now that we are into this thread if I remember right, lime is what will leach out, but I can not remember if that is good or bad, and maybe that is the reason for the long soak.
Lime is a good thing in moderation. (Kalkwasser) There would likely be a lot in the beginning hence high pH.
that guy that has had his tank for like 35 years has piece of asphalt in his tank. i belive he got it from the ocean so if u cured it long enuff im sure it will be fine
thanks everyone.
i think im just going to substitute the blocks for plastic egg crate.
i really do not feel like waiting a month while the concrete cures... but it does sound like a good idea for the future.
There is a thread some where on do it yourself baserock. I did this earlier this summer and have a bunch of it curing at my house right now. You need portland cement type II, and mortons water softener just make sure it is straight NaCl. I just tried to eye ball a mix ratio of about 4 parts salt 1 part cement. But i added too much salt and i dont think the rocks will be that strong. Maybe shoot for 3-1, just play around with it. I will let you know how my rocks turn out when i get back from china in a week.
tropicorum uses lots of cinder blocks in their greenhouse tanks/trays whatever they are called. that and corrugated fiberglass sheets like for carport roofing