It was me that posted on another forum about this ladies use of John Innes 3. and my concerns have been misrepresented somewhat.
particularly this:
He mentioned that it's deadly to use with fish, and that it should never be used in hard water or with a cap of 2mm, or under hardscape.
my concerns were based solely on
her description of her set-up.
She said she had put
3 inches of no.3 under 2 inches of sand. Also, looking at photos of her tank it 'appeared' that the no.3 was also under her rather large rocks.
Over two posts I pointed out that this was probably too deep and she was risking anoxia within the substrate and H2S production. I advised her to poke the sand so that the overlying water could get down into the soil. and so admit Oxygen and thus prevent H2S production.. at least until the plant roots can get down there and do the same.
She said she lived in London.
I pointed out that no.3 contains crushed limestone and this could impact her water parameters.
Those were my two main concerns. H2S production and possible alterations to water chemistry.
She also stated that No.3 has no peat in it. I pointed out that this was incorrect, in fact no.3 is approx a third peat by volume.
In a subsequent reply.. her description of her tank set up changed completely.
the inches became millimetres/cenitmetres. so, 3 inches of soil across the entire base of the aquarium, became 1mm to 3cm of No3. Obviously this changed everything. poking the soil was still a good idea, but there was much less chance of it being problematic.
I also mentioned the additional 'Superphosphate' and 'Potassium Sulphate' that is added to No.3 by the blenders. it seemed unclear as to whether she was aware of this addition. I made her aware so that she could adjust her ferts regime to take the extra in the substrate into consideration. I don't even pretend to be an expert on ferts in high tech tanks.. but it did seem pretty obvious to me that the chemicals in her soil could adversely effect the ferts she was adding. possible overdosing? My intention was to prompt her to look into this side further. Ask people who are better equipped to answer these concerns than I am. they might mock me for being over cautious. thats fine.
In a subsequent private message to me she stated categorically that she wasnt going to add fish to her tank. It was going to be a 'planted tank'. My eyes popped at that. had she said this in her original posts then my concerns (about Hydrogen Sulphide) would have been nullified. I would likely have said nothing aside from mentioning the chemicals that are in No.3. its peat and limestone components. and that due to the latter she should keep a close eye on her hardness and PH parameters. She may have had problems with her plants due to overdosing going forward.. but thats easily dealt with. poking the substrate is a good idea at least in the short term. H2S is deadly to fish... but it also kills plant roots I believe.
My responses to her were all made in good faith. I am extremely uncomfortable about the use of gaseous CO2 in aquaria that house fish. but.. her use of that method had nothing whatsoever to do with my responses. which were solely to do with the depth of the substrate she had chosen and the possible problems this could cause.
being at least aware of these potential problems is a first step towards early recognition. making it easier to deal with before the house of cards comes tumbling down.
Purely as an aside:
Over the past several months I have been asked many times about appropriate soils for a "Walstad" or "natural planted tank/NPT" set up. John Innes No3 is always in the top 2/3 choices of easily available soils. but. Im always careful to mention what is in it. do you want peat? do you want Limestone? do you want superphospate and potassium sulphate? (Those last two are easily dealt with)
I generally favour John Innes 'seedling' which has none of the above chemicals. or 'pond soil' or even Top Soil (my own choice) but many people use No.3 and in fact Walstad mentions it herself as a viable alternative.
To suggest that i consider it 'Deadly' is ludicrous.