Cheers homies!
Derek, you're way to kind mate-
-- you'd make a campaign manager!
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Ice, diatomaceous earth is good against many pests; it's a sedimentary "rock" made from the structural "shells" of single cell algae, which form mind blowing complex and intricate structures to help them stay afloat (look diatoms up sometime)... it's made pretty much of glass--SiO2, though some use CaCO3,... at the microscopic level, it's like a collection of shards and pointy bits that can cut and pierce through tender spots, externally or internally, plus it acts as a type of dessicant too,...point is, it's a mechanical/physical pesticide.... putting a layer on the soil surface forms a barrier against vermins! Fungus/soil gnat adults are harmless, they're basically just flying gonads, it's the larvae, in mass, that can do the real damage, eating roots.... breaking the life cycle is the key, but often, there are more around to replace those that are nailed! this is why I like the Bt treatment, it can last,... DE will work for a shorter period, but it can soon get washed out after watering a few times, mixed into the soil more, and you don't want to overdo the covering or it can form a clay-like barrier on top, messing with water penetration,... I'd say try the Bt first, and skip the DE for now, but if you like, go ahead and get some DE and apply after you water the Bt in,... surface covering with DE should be about 1/8"+, no more than 1/4",....
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Skuff-- low level infestations can be hammered out the hard way, like you did,... as mentioned, it's about breaking the life cycle, and preventing new adults from dropping more eggs! Small infestations are not problematic, only when the population becomes big do the maggot-like larvae cause sufficient damage to harm the plant...
...pH'ing water isn't necessarily a locked-in rule, unless it's pretty far off (alkaline), which indicates high hardness (lots of dissolved mineral content, CaCO3),... Some lucky folks have naturally softer water, and good pH, which is always great! between this, and the right type of nute (self buffering), and well limed soil, you can get away with little to no pH management, but few are so blessed... and when trouble comes, without the right info and pH, etc., it can be difficult to fix the problem, and not make matters worse... Mineral build-up from hard water may screw with pH at some point, though with all the acidic inputs from nute's, it's less common than overly acidic soil,... Do you have a TDS meter, and a pH meter? Just curious about your water,... Chlorination does kill the soil herd, make no mistake,... this is far more critical if using organic nutes vs synthetic,.. the latter has nutes in a form readily absorbable by the plant, the former needs the soil heard to break down and convert the organics into available forms,... so, yes, you can water with chlorinated water, while using synthetics, and it won't really hurt the plant, but it's a compromise whether it's apparent or not,... lack of a decent soil herd has many other consequences as well, relating to other potential soil pathogens, disease and other nutrient issues,... Also, some treatments for water use chloramine, not a gas, so it won't gas off,.. that requires time in the sun the break it down, or treatment with fish aquarium neutralizers,... Did you say you're using an organic nutrient line, that self buffering? Which one? .... pH'ing the nutrient solution depends on the products used; some can self-buffer
in solution, but that doesn't extend to the entire soil/root zone,... pH altering inputs are coming in from the soil, soil herd and plant itself, it's a very dynamic thing down there,... what buffering is in the nute solution won't carry over much to the soil, but keeping the pH from water and nutes in proper ranges to begin with goes a long way toward longer term stability,...