White pimple like spot on discus - should I be worried?

Hi,

One of my larger Stendkar discus has pimple like spot near its top fin on its back. (Pictures below). The same discus also has a red spot inside its lower mouth. Not sure if I should be worried so I have increased the temperature from 30C to 32C and have dosed tank with API melafix and pimafix.

Fish in tank are 3 medium sized Stendkar Discus and 2 juvenile Stendkar Discus, 1 Angelfish, (1 guppy, 4 fivebanded barbs and 1 male betta - these were original fish before Discus introduced 9 months ago).

180L tank, gravel substrate, few ornaments, external fluval 207 filter (planning to change to oversized Oase filter soon because keeping discus), LED lights, new Pothos plant (4-5 stems) just introduced 2-3 weeks ago and growing. Tank established Jan 2021. Perform 50% water change weekly plus gravel vac and monthly filter clean (last done 3 weeks ago). UV lamp via filter runs 6 hrs per day. No new fish added in the last 6 months.
Ammonia - 0
Nitrite - 0
Nitrate - 60-80? (tap water comes out as 30-40 - tried pozzanni nitrate filter in past but does not last more than a few weeks hence opted for Pothos plant to reduce/control nitrates)
pH 7.6 - 7.8

Fish are fed twice a day with Stendkar brand beefheart and three times a day with Sera Discus Granules.

Thank you in advance to all that reply.

First off, a male betta should never get kept with any other fish. Even if they seem fine now, all it takes is the smallest interaction and your betta will snap and attack. If he attacks your guppy or barbs, he’ll likely kill or injure them. If he attacks the discus or any others, he’s very likely to get injured or killed. I would remove him to his own tank ASAP.

And you’re keeping multiple discus in a 47 gallon tank?? These fish get to be VERY big and need a big tank!!

The white bump on the body could be excess mucous or the start of a sore/ ulcer. Monitor it over the next few days and post new pictures if it changes.

Unsure about the sore in the mouth.
Can you post more pictures of that?

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Reduce the beef heart and use prawn and fish instead.

Add some floating plants like Water Sprite to offer some shade and help use the nutrients, thus helping keep the nitrates lower. The pothos plants should also help with nitrates.

Add some Ambulia and narrow Vallis to the tank to help provide more hiding places for the smaller discus, who looks stressed out, as does the angelfish.

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Increase the size of the water change to 75% or do two x 50% water changes each week. It will help keep the nitrates a bit lower while the plants start to grow.