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Possible In-tank Bleach Process (long post)

Last week I visited a hydroponics solution manufacturer to have some 
fertiliser made up. He had a tank set up for testing the effects of 
fertiliser residues - Australian rainbowfish and goldfish, no plants, 
internal power driven sponge filter. The tank was unlit but placed near a 
window. It wasn't getting brilliant light at the time I was there but may 
at other times of day. He indicated that he had phosphorus levels of 
around 40-50 ppm and there was minimal algae. His "secret" was the use of 
a "stabilised hydrogen peroxide solution" called Hy-San at 5 ml per 10 
Litres of tank water, but said it was not possible to dose to that 
concentration in one dose - you had to build the dose over some hours or 
you ended up with over-oxygenation of the water and fish deaths. He was 
at pains to say that it is not sold as an algicide and that he was not 
recommending its use in aquaria, but that he found it effective. He is 
not maintaining planted tanks and could not comment on its effectiveness 
in them from first hand experience but said it did not harm terrestrial 
or hydroponic plants.

I bought a litre of the solution and dosed a small 2 foot tank (around 60 
litres) with 25 ml of the solution in 3 installments (one a day for 3 
days) on Saturday, Sunday and Monday. This tank gets morning sun light 
from a window and has a 20 watt compact fluoro - the sort sold to replace 
incandescent bulbs - in a desk lamp fitting above it on timer giving 8 
hours per day. It had some beard algae on water sprite and a couple of 
Anubias Nana. It has 2 Betta Imbellis, 2 Croaking Gouramis, a Ram, and 4 
Bronze Corydoras. The tank isn't a "display tank" and I haven't been 
worried about the algae overly, but I felt more comfortable about testing 
on that tank than my other which is in the living room and has freshwater 
shrimp in it.

It is now Tuesday evening and there is significant reduction in algae 
with no signs of adverse effects for plants and fish though perhaps it is 
still too early to be totally certain about adverse plant effects. Plant 
leaves are bright, the algae on the water sprite has died and rubs off 
easily. I think it might have been a different algae on the Anubias. This 
one doesn't rub off but doesn't look the same as it did and I suspect it 
has died also. I haven't used the chlorine bleach wash so I can't comment 
on comparison of appearances.

What this solution contains is 12% H2O2 and less than 0.030 grams/L 
colloidal silver. Some of the details from the label say:

"Hy-San destroys bacteria, fungus, virus pathogens and Chlorine through 
oxidation.

Advantages:

- Oxygenation of plant leaves and roots.
- Reduction in Algae and Mould growth.
- Active over a wide pH range.
- Has a rapid long lasting sanitation action.
- Compatible with water soluble fertiliser

Hy-San is compatible with all other nutrients and pH levels for all 
sanitation needs in the Horticultural Industy.

Hy-San assists in the sanitation of nursery potting mixes and is ideal 
for all substrate, perlite, rockwool media, potted pot plants, orchids 
growing in bark, spaghnum moss and the practice of wick watering, eg 
African Violets, foliage plants and for use in hydroponic nutrient tanks.

Hy-San is especially beneficial when used with a regular water 
maintenance program at the recommended rate, reference to label 
recommendation. This allows plant roots to access dissolved nutrients 
freely, whilst creating a biological balance in oxygen poor growing 
medias limiting the development of pathogen growth e.g. Pythium, 
Rhizoctonia and Sclerotinia and other water borne fungal disorders e.g. 
hydroponics systems.

Hy-San is a beneficial aid during propogation in the preparation of soft 
wood, medium and hard wood cuttings and other delicate leaf cuttings to 
maintain freshness when sprayed with Hy-San.

...

Comment:

Over sanitising will have no adverse effect on plants or equipment, 
however, this practice is not recommended. ..."

I've left out some of the label dealing with doses for various purposes, 
safety (it's corrosive and a skin and eye irritant), first aid etc.

Others have posted on the use of chlorine bleach in a wash outside of the 
tank. This may be a good alternative for in-tank use.

My reservations about this technique at present are the colloidal silver 
and possible effect on biological filtration. I have no idea on toxicity 
effects for silver with fish or invertebrates. At the recommended dosing 
rate, the silver level would be less than 0.0000015 grams/litre or 0.0015 
mg/L by my calculation (I may have the maths wrong). Perhaps someone can 
comment on silver toxicity. I don't know what the role of the silver is 
but the hydrogen peroxide is described as "stabilised", meaning it 
doesn't decompose as rapidly as normal hydrogen peroxide does. It may 
assist in the anti-bacterial action of the product, or it may assist in 
stabilising the peroxide. It doesn't seem to have had an effect on the 
fish but I don't know what the effect on the freshwater shrimp in my main 
tank would be and I have no intention of trying it out at this stage. I 
also don't know what the effect on biological filtration is but I suspect 
it can't be too bad. I wasn't overly worried in the 2 foot tank since it 
has a fair amount of plants and I've actually run the tank for long 
periods without a filter, just relying on the plants. The fish in the 
test tank I was shown all seemed healthy and there were no plants there 
so I assume the sponge filters were functioning satisfactorily.

I guess that's it for what I can report at this stage. I would recommend 
caution if anyone wants to try this technique but I thought it was worth 
posting to see if anyone else has used hydrogen peroxide as a bleach for 
algae eradication, or if anyone could comment on the effects of silver in 
aquaria. The peroxide itself will decompose to water and oxygen, neither 
of which is a problem, so the technique should lend itself to in tank use 
if there are no longer term problems with the silver. I wonder what the 
effects of ordinary hydrogen peroxide without silver would be.

Any comments?

David Aiken