A few things jump out here.

First, Masteron is not a diuretic, and it does not guarantee a “dry” appearance. It may create a harder cosmetic look when someone is already extremely lean, but it cannot reliably cancel the sodium and water retention caused by testosterone, GH or other variables. If increasing testosterone above roughly 220 mg consistently softens your appearance, that may simply be your individual response to that dose.

Second, gaining five pounds during the first week of GH is almost certainly fluid, glycogen and possibly increased intestinal content not five pounds of new tissue. Fluid retention is a known, dose-dependent effect of GH. It may lessen after your body adjusts, but there is no guarantee that it will disappear while the dose remains unchanged. If it persists, the medically sensible response is to discuss reducing or discontinuing the GH not adding a diuretic or manipulating electrolytes to fight a drug-induced side effect.

I would also confirm that this is genuinely extracellular water:
Compare seven-day average weight rather than individual weigh-ins.
Measure your waist under identical morning conditions.
Look for swelling in your fingers, ankles and lower legs.
Track blood pressure.
Note numbness or tingling in the hands, which can accompany GH-related fluid retention.
Keep carbohydrates, sodium, water and meal timing consistent.

The stomach and lower back are also common places to hold body fat, so softness there does not automatically mean water. If you are not truly stage lean, chasing a “dry” appearance with more drugs usually does not work. Masteron tends to reveal conditioning; it does not create conditioning.

As for competitors running high testosterone and still appearing dry: some tolerate it better, some run less testosterone than they admit, some are exceptionally lean, and some use increasingly risky drugs or diuretics. Their appearance does not prove that their approach is safe or that it will work for you.

I would not start cutting water, eliminating sodium, loading potassium or adding a diuretic. Extreme water and electrolyte manipulation can cause cramping, arrhythmias, kidney injury and potentially life-threatening sodium or potassium abnormalities. Keep sodium and water consistent. Also clarify whether that 3,500 mg of potassium is your total dietary intake or supplemental potassium do not independently supplement large quantities simply to balance sodium.

If five pounds arrived rapidly after introducing GH, the new drug is the obvious variable. Depending on the severity, the rational choices are observation, dose reduction or stopping it not adding another compound to conceal the side effect. BTW this is a common side effect most describe when taking GH and most opt to put up with it.

In short: get genuinely lean, use the lowest drug exposure you tolerate, keep water and electrolytes consistent, and stop expecting Masteron to function as an anti-estrogen or diuretic.

Bit high of sodium intake for running gh, no? Also I feel much better at 800mg mag. Less sore, better mood, sleep. Ran 400mg for years, the difference is night and day. We're all different. Anyhow, your situation, heres a question, what is your daily carb intake like??