W/C's and drop in SG

[scsi]

Originally Posted by bv_reefer

wow 4pg's..thats a new record for me..usually people give up at 2-3 , but seriously could this be the reason that i still have cyano bacteria, because i use fresh RO water?

well..... you really stepped into it this time
so to speak.......

[Aquattro]

let's clear something up here. By water change, do you mean you are siphoning out 5 gallons and replacing with a new 5 gallons? Or did you let 20% evaporate and now you topped it up? There is a big difference.

[bv_reefer]

nono i siphoned out 5 gallons and put a clean 5 gallons in...just fresh water though

[Rippin]

Originally Posted by bv_reefer

nono i siphoned out 5 gallons and put a clean 5 gallons in...just fresh water though

Right, there's the problem. As you are most probably aware by now, you need to replace the siphoned 5 gallons with saltwater at the same SG.

ok, I think this thread is done now...

[Aquattro]

Originally Posted by bv_reefer

nono i siphoned out 5 gallons and put a clean 5 gallons in...just fresh water though

Ok, that is wrong. You need to add 5 gallons back of salt water of the same SG as you removed.
Now that we've cleared that up, you need to determine what the SG is now, using reliable equipment, and adjust if neccesary.

[bv_reefer]

i already knew my SG, it's 1.023 and i just made my 5-gallon of w/c water at 1.023 SG, so now i can do actual water changes

[Aquattro]

Originally Posted by bv_reefer

i already knew my SG, it's 1.023 and i just made my 5-gallon of w/c water at 1.023 SG, so now i can do actual water changes

so there we go. But you mentioned your RO water was 1.021 or something, which it certainly was not. So if your hydrometr said it was, you need a new one, or different RO water. RO is always going to be 1.000. Then you add salt to 1.025 (my preference) and then add to the tank. Take some water to the LFS to double check your readings.