1 JUNE 1999
Date: 06 May 1999
From: Jennifer E. Collins <JCOLLINS@cadmin.nsac.ns.ca>
To: <AQUA-L@killick.ifmt.nf.ca>
QUESTION:
I am trying to grow shellfish larvae, but I haven't had any success
in getting them past trochophore stage. I think it may be a problem
with my water quality. I am using 100% Instant Ocean for my
seawater. I chemically sterilize the water using bleach and
neutralize with sodium thiosulfate. I then run the water through a
UV filter and a 5u particle filter. I have just noticed that when I
use the UV filter, the water becomes discolored (yellowish) and
smells of sulphur. When I bypass the UV, I do not have this problem.
Is there a chemical reaction I am unaware of?
Jennifer E. Collins
Shellfish Technician & Algologist
Nova Scotia Agricultural College
P.O. Box 550
Truro, Nova Scotia
B2N 5E3, Canada
Tel: (902) 893-6533
Fax: (902) 897-9399
<jcollins@cadmin.nsac.ns.ca>
***************
COMMENTS 1:
The yellowish color and the sulfur smell are usually associated with the end point (or excessive use) of sodium thiosulphate to neutralize bleach. The UV system may be reacting with any extra thiosulphate that is in the system. I would check the calulations for the amount of thiosulphate. Use a chlorine test kit to determine the level of chlorine before you go to neutralize it. As the chlorine oxidizes organics within the water, the level of free chlorine will decrease and you may be over dosing the thiosulphate resulting in possible problems.
David Cripe
<DCripe@mbayaq.org>
***************
COMMENTS 2:
Personally I would stay away from either chlorine and UV.
Try microfiltration or pasteurization. They leave no toxic
residuals. Chlorinated organics can be toxic. For instance
if you have a nitrate load you will generate nitrosamines.
The algae won't mind, but the larvae will.
Sodium thosulfate is a great bacteriological medium so
use it sparingly.
UV is a mixed blessing too. If your contact time is only 95%
effective in killing the bacteria, you can stimulate an
unbalanced bloom of some heterotrophic species chowing
on all the fresh organic matter of all of his dead cousins.
I prefer cleaning with hot water and trying to maintain a
healthy natural flora by spiking with one of those "probiotic"
mixes.
Robert B. Rheault, Ph.D.
Moonstone Oysters
Narragansett RI, USA
www.moonstoneoysters.com
<oysters@ids.net>
***************
COMMENTS 3:
Lose the sodium thiosulfate. Any unreacted sodium thiosulfate residue is highly toxic. I have seen more organisms killed with sodium thiosulfate than any other single material in aquaculture. If you must use chlorine, gas it off or break it down in sunlight. Ozone is probably a better choice than chlorine anyway or use nothing at all and balance your closed system with probiotics.
Durwood Dugger
BioCepts Intl., Inc.
<dugger@gate.net>