Since you can look at it you will be able to see the difference. Tonga is usually branch shaped, long and thin. Fiji may be a little more dense than Marshall Island, maybe not. They should be able to tell you if one is denser than the other. I prefer rock that is more porous. You get more volume per pound and is is a better nitrate filter. For me a lot of my decision depends on price. I get mine from a local dealer for around $4/lb. There isn's an
LFS around here that can touch that, even double that. You can usually get
LR online for $3-4 delivered if you buy a large enough quantity.
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