Tank currently struggles hard against Hovers. Tank has been in a poor spot balance-wise ever since Emissary got nerfed, completely lacking in cheap raiders or a skirm making its game completely fall apart if its uber-raider (Kodachi) fails.
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I would recommend hiding Emissaries next to stingers. Gradually kill those scalpels from range, once you've pushed them back then build another Stinger closer. Maintain an army to deter them attacking the Stinger (if they push the stinger then push back).
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At your level a Cyclops will also work to kill Scalpels. Use the Cyclops to kill a couple then pull it back for repairs. Have some Kodachis or Ogres on hand to intercept if they try and rush down your Cyclops with the Scalpels.
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Lotus also works well against both moderators and Scalpel, slowing them down with its hp and doing damage. A Lotus forest can absolutely brutalize a moderator/scalpel swarm if your opponent doesn't micro well
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There's also just deciding to spend the 700 on another factory and getting a cloakbot factory for the Glaives and the Iris area cloaker (sneaking a bunch of Ogres up to the Skirmisher ball works very well indeed!). You can also just make a static area cloaker and morph it into a walking one.
A similar strategy should work against Moderators as against Scalpel: Either pure Kodachi swarms (hoping to overwhelm whatever riot force they have or just avoid the skirm+riot ball and hit the enemy base) or Emissary in a Stinger nest or a Cyclops slowly killing them all or a factory switch or an area cloaker on Ogres.
Contrary to
Amnykon, I would NOT recommend Ogres. They are not a cost effective solution (seen in both real games and tested in sandbox) and will lose cost for cost.
If you are a micro god and can throw in a Welder/Minotaur to tank shots just before the Ogres come in to range of the Scalpels it
may trade evenly, but if you get the timing even slightly wrong it'll backfire horribly with the Scalpels turning early and you'll lose all your Ogres without killing a single Scalpel.
Kodachis work much better against Scalpels, though even pure Kodachi will only trade evenly with a Scalpel+Bolas ball.
Contra
GoogleFrog I would also not recommend sending Minotaurs against either Moderator or Scalpel (though they are good against turrets, which may have been what he means). It tends to die after killing one or never get in range to kill one at all (if you retreat early). Instead, send a single Minotaur with a retreat percentage (and retreat zone) set (or, instead, a welder or two) slightly before a big Kodachi swarm (as many Kodachis as the enemy has skirmishers should work).
Note that if you have too few Kodachis and/or the enemy has some decent rioting (Bolas or Mace or somesuch) then you could just lose everything for no gain, so this is risky... Hence me not including it in my recommended strategies above.